15: The consequences of living with geology: A model field trip for the general public
Published:September 07, 2016
- PDF LinkChapter PDF
David M. Abbott, Jr., David C. Noe, 2016. "The consequences of living with geology: A model field trip for the general public", Unfolding the Geology of the West, Stephen M. Keller, Matthew L. Morgan
Download citation file:
The geology of any particular area imposes constraints on what humans can do. These constraints are generally thought of as geologic hazards, but access to the natural resources we all use and to recreational or scenic areas, may be local issues as well. The location of roads, bridges, reservoirs, landfills and other waste-disposal sites, etc., also have both geologic and public-policy consequences.
As a society, we can either plan for or fail to plan for these consequences. If we allow people to build homes in floodplains, they will become flood victims. If we prohibit building on floodplains, we have impacted the value of those lands. Whose ox gets gored, how and when? Who pays? This trip won’t offer answers to these questions, it simply will point out that these are issues that ought to be debated and that we, as geologists, can contribute technical information relevant to the debates.
The field trip will travel south along the central Front Range mountain front from Marshall to the US-285 roadcut at Turkey Creek with stops to look at burning coal seams, at the differences in mineral mining between Boulder and Jefferson Counties, to reflect on mountain flooding and the possibility that Leyden Gulch could capture Coal Creek, to look at the large rocks falling off the mountain and traveling through housing, at the Red Rocks Amphitheatre as a scenic area where geology is described for the public, and at the fossil oil reservoir and roll-front uranium deposit exposed in the Dakota sands.
The Concept of This Field Trip as a Model Field Trip
This field trip is a model for the type of field trip that we, as geologists, ought to be running far more frequently in each of our communities for the general public, service clubs, politicians, school groups, religious groups, etc. The geology of any particular area imposes constraints on what humans can do. These constraints are generally thought of as geologic hazards, but access to the natural resources we all use, from sand and gravel pits to water resources to oil and gas wells to large open-pit mines to particularly scenic areas, may be local issues as well. The location of roads, bridges, reservoirs, landfills and other waste-disposal sites, etc., also have both geologic and public-policy consequences.
As a society, we can either plan for or fail to plan for these consequences. If we allow people to build homes in floodplains, they will become flood victims. If we prohibit building on flood-plains, we have impacted the value of those lands. Whose ox gets gored, how and when? Who pays? We won’t offer answers to these questions, we simply will point out that these are issues that ought to be debated and that we, as geologists, can contribute technical information relevant to the debates. As geologists, it is important that such trips be as neutral as possible on the issues addressed. We can advocate either science or policy but not both without being viewed as having a conflict of interest (Abbott, 2000). The goal of these trips is general education, not advocacy of a particular policy.
Discussion points are included in the text to address specific consequences of living with geology and related policy questions. Use of a different font, in this case Helvetica, helps separate the policy questions from scientific observations. We suggest that trips based on this one use a similar method to separate geologic and policy discussions.
Every area has technical field trips that can be adapted for non-technical audiences and decision-makers. The key adaptation is a shift in focus away from details of interest only to technical specialists, and toward larger topics that impact the public. Technical details, although usually simplified for this type of audience, become supports for the goal of addressing how geology affects people at the site in question.
Stops are selected as illustrations of particular issues and, generally, for ease of access by those with limited physical abilities. Variations of this trip have been run for different target audiences. Participants have included teenagers, who showed real interest in some of the topics.
This text is the sixth edition of this trip; the first edition being Abbott and Noe (2002). The 2002 edition was developed from, and incorporates portions of, the original text from Noe et al.’s 1999 GSA field trip, “Bouncing boulders, rising rivers, and sneaky soils: A primer of geologic hazards and engineering geology along Colorado’s Front Range.” The third edition was a trip conducted for the Dartmouth Association of the Rocky Mountains in 2010. Some stops from that trip have been deleted, and others have been added to expand the scope of topics examined, while keeping the trip within a manageable time frame. Changes in both earlier editions and this edition include updating the text to account for continuing changes in highway interchanges and housing development, inclusion of additional figures, deletion of the Colorado School of Mines stop because of redevelopment— we’ve retained some “in memory of a former stop” text—and the consequent addition of different stops. These text changes reflect the continual changes in our environment, which require that guides be continually updated.
Introduction to This Particular Trip
The Colorado Front Range is spectacular because of its geology, but this geology has consequences for those of us who live here. The region is known for sweeping vistas and scenic river canyons; however, many residents who frequent the natural areas of Colorado also desire affordable gasoline, electricity, building materials, water, as well as building sites with gorgeous views, no radiation, and no trash. This trip will focus on the realities of these desires and the degree to which they can, and cannot, be achieved. Furthermore, the trip will focus on various geologic characteristics of the mountain front and how they impact land-use planning and the lives of residents.
Although this trip is similar to the technical field trips taken by professional geologists, it is designed to inform non-geologists with enough basic earth science to understand why the issues presented are important, and to engage them in some reflection about the consequences of various policies (or lack thereof) in land use.
This road log contains detailed directions from point-to-point along with pertinent observations and questions about what will been seen and discussed. The trip route is shown in Figure 1. When using this guide on individual trips, have someone other than the driver in each car read the road log as the trip progresses. Although the focus here is on what we will see, the log contains various notes on similar problems in well-known areas around the Denver metropolitan area and the state. Table 1, placed at the end of this guide (p. 376) for ease of reference, is a generalized stratigraphic section of the Denver metropolitan area.
Generalized Stratigraphic Section For The Colorado Piedmont, Morrison Quadrangle (Modified From Scott, 1972)
Points of discussion and related questions are included throughout this field guide. Individually, each of us may or may not agree on suggested answers to the problems and questions raised by these points. Nevertheless, we should think about them. Geologic events occur whether we plan for them or not. Additional discussion points may occur to you; please share them with the group on the trip.
It is useful to look at past geologic events as a means of planning for future events and their impact on present and future development. The Colorado Geological Survey (CGS) has a statutory mandate to assist local governments with planning issues involving various aspects of geology. Since the early 1970s, CGS geologists have reviewed plans for thousands of subdivisions along the Front Range and elsewhere within the state. The CGS has provided emergency assistance and advice for incidents involving geologic hazards, in addition to research and mapping of general geologic hazards and other geologic features (e.g., Soule et al., 1976, on the Big Thompson flood; Soule, 1978, on Douglas County; and Noe, 1997, and Noe and Dodson, 1997, on heaving bedrock hazards). Geologists from the U.S. Geological Survey, local colleges and universities, and private industry have all contributed to our knowledge of the geology of the Front Range area.
There are thousands of pages of technical literature relating to various aspects of the geology we will see during this trip. But that is too much information, even for most professionals. If you want to know more, please refer to the various references are listed at the end of this log. One publication written for the general public may be of particular interest: The Citizens’ Guide to Geologic Hazards (Nuhfer et al., 1993), which is available from the American Institute of Professional Geologists (www.aipg.org/Publications/listofpubs.htm). State geological surveys frequently have publications written for the general public on particular issues, for example, Noe et al. (1997), Heaving-Bedrock Hazards, Mitigation and Land-Use Policy, Front Range Piedmont, and Noe et al. (2007), A Guide to Swelling Soils for Colorado Homebuyers and Homeowners, which is given by builders to buyers of new homes in Colorado.
General Geologic Setting
This trip extends from the hamlet of Marshall, just south of Boulder, down the eastern margin of the Front Range to the Turkey Creek water gap, where U.S.-285 and Turkey Creek come through the Dakota Hogback (Fig. 1). The route roughly follows the topographic transition from the interior of the North American continent to the Rocky Mountains. This topographic transition reflects the geologic transition as well. To the east, the landscape is generally flat all the way to the Appalachian Mountains, and is underlain by sedimentary rocks that are more or less flat lying. To the west, the hard, crystalline rocks of the Front Range rise dramatically.
Along the mountain front, the sedimentary rocks have been folded and faulted from approximately horizontal to steeply angled (dipping) or vertical (Fig. 2) (Weimer and Ray, 1997). Much is known about this transition from the Great Plains to the Rocky Mountains in terms of the details and the timing of various tectonic events. Continually acquired new data answer some questions and raise more, for example, why is Colorado at a high elevation and when did this uplift occur? (Reynolds et al., 2007, particularly their figure 9). However, today’s trip focuses on geologic hazards and other geologic features affecting land use.
Trip start:This trip begins at the Colorado Convention Center. However, for future use of this field guide, the zero point for mileage is the Marshall Mesa Trailhead parking area, just east of the intersection of Eldorado Springs Drive and CO Hwy. 93 in Marshall (N 39° 57.10’, W105° 13.51’), Stop 1.1
The latitudes and longitudes used in this road log use the WGS 84 geoid. This is the same geoid used by Google Earth™, so stops and roads can be readily viewed in Google Earth.
Directions to Stop 1:Leave the Colorado Convention Center at 14th Street between Stout and Welton Streets by turning right on 14th Street. Proceed 1 block to Glenarm Street and turn right. Proceed two blocks and turn 45° to the right onto Colfax Avenue. In one block, turn right onto Speer Boulevard (north) and continue to the 1-25 north exit 2.7km (1.7 mi) from the Convention Center. Continue on 1-25 for 8.2 km (5.1 mi) to the exit onto US-36—Exit 217A to Boulder (west); the exit is from the left-hand lanes. Exit US-36 at the Superior-Marshall (McCaslin Boulevard) exit, at 33.8 km (21.0 mi) from the Colorado Convention Center. Turn left and cross over US-36, then turn right on Marshall Road (CO-Hwy. 170) at the Superior Marketplace. Proceed 6.4 km (4.0 mi) to the Marshall Trailhead parking area entrance (N 39° 57.21’, W105° 13.88—this intersection is the zero point for subsequent mileage measurements). Turn left into the trailhead parking area and walk to the east end overlooking Marshall. This is Stop 1.
Roll-By Points of Interest on the Way to Stop 1
Development pressure along the Colorado Front Range: The Denver metropolitan area and other urban areas along the Colorado Front Range piedmont were founded, and started to grow rapidly, following the initial gold rush in 1859. The city of Denver, named after a Kansas territorial governor, was founded in 1859. The coming of the railroads greatly accelerated this growth and a secondary service economy ensued that accelerated after the Civil War. William Jackson Palmer, a Civil War general, founded the Denver and Rio Grande Western Railroad (now part of the Union Pacific) and the city of Colorado Springs around 1870. Precious metal mining and the near-instant appearance of mining camps in the mountains, and coal mining, agriculture, and water development on the piedmont were responsible for most of this early rapid growth. This continued unabated until the decline of the metal-mining industry following the silver crash of 1893. Many mansions, commercial buildings, and churches were built during the late 1880s. Construction of the Colorado State Capitol commenced in 1890. Many of these buildings are built from Colorado native stone and are the focus of an interesting tour for a geologist (see Murphy, 1995). Colorado, the Centennial State, was admitted to the Union in 1876.
A century later, this area experienced rapid growth following World War II and during the regional “energy-boom” years of the mid-1970s to early 1980s, a “bust” from ~1984 to the early 1990s, and another boom accompanying national trends that (arguably) continues until the present despite setbacks resulting from the dot.com crash of 2000-2002 and the recession of 2008 and following years. The regional population around Denver is now (2015) estimated at ~3.3 million and the total Front Range regional population at ~5.0 million.2
The Front Range regional area or urban corridor encompasses the communities extending from Cheyenne, Wyoming, through Fort Collins and Greeley to Pueblo on the south and from the bedroom communities in the foothills to the west to the contiguous eastern suburbs in Colorado. An area from Cheyenne, Wyoming, on the north and Pueblo on the south will soon be included in the contiguous urban corridor if present growth rates continue.
The predominant style of residential growth in this region is now single-family tract-housing development on lots ranging in size from ~3500-8000 ft2 (1/10-1/5 acre, or 325 m2 to 743 m2) with its attendant interspersed infrastructure. In recent years, the tendency has been toward construction on smaller lots with multi-story houses. This has probably slowed the per-capita land consumption by development somewhat, but not its overall rate or amount. A tendency has been for infill of this higher density residential development among older lower density residential and agricultural land uses along the urban fringes.
Discussion Points—Development Pressure
Debate over growth in and along the Front Range corridor has been raging for years. US-36 between Sheridan Boulevard and Boulder was all range and farmland (with the exception of a much smaller Broomfield, now the metro area’s newest city and county) until about 20 years ago when it started filling in. This pace has accelerated in the past 10-15 years and now little range and farmland is left and is rapidly disappearing into residential tracts, office campuses, and shopping centers. The formerly adequate four-lane highway originally completed in 1951, which had only the Broomfield exit between Denver and Boulder, is now overcrowded and new exits and toll lanes have been added. What you see along US-36 is typical of the growth occurring between Fort Collins to the north and Colorado Springs to the south, particularly along I-25.
The growth debate revolves around ways to preserve open space. At the same time, an expanding population, driven primarily by people moving into Colorado, demands affordable housing and convenient schools, grocery stores, other services, shopping, and nearby jobs. One side of the debate urges greater population densities requiring less acreage, increased reliance on public transportation, and other measures to control growth. The other side of the debate is marked by the rapid sales of newly developed mostly single-family homes with yards on the margins of urban areas, where land is cheaper as are resulting home prices on a per square foot of living space basis.
Land prices are climbing in the central urban areas. “Scrape-offs,” the practice of buying an older home, tearing it down, and building a new home that often occupies most of the buildable area of the lot, is increasingly common in the older, urban areas. Similarly, construction of row town-homes and apartment complexes changes the character of a neighborhood. These changes are increasingly vigorously opposed by neighborhood groups. Neighborhood groups likewise oppose new or expanded transportation corridors, saying “Build these in someone else’s neighborhood!”
Regulations added to building codes to increase health and safety are well intentioned but have the consequence of adding to building costs. Affordable housing for not just the traditionally “poor” groups, but also an increasing percentage of the “middle” class is becoming an issue as housing costs increase. People are “voting” with their money and cars to move farther and farther away to the suburban margins. Most people still prefer to raise their families in single-family residences surrounded by yards with grass. The consequences are increased demands for water, increased forest fire hazards as development expands into the mountain foothills, and conflicts with the oil and gas industry as housing developments move into areas of wells that have been producing for years and in which new exploration is occurring in different stratigraphic intervals (rock layers) in the same areas.
Water availability is another serious issue. The Front Range urban corridor sits on the edge of the High Plains, in an area that explorer Stephen H. Long called the Great American desert (this was prior to penetration of the Basin and Range and Colorado Plateau). For years, Colorado has had water courts debating water rights and their transfer. Growth exacerbates this problem. Downstream states and Mexico want their water as well. Unfortunately, despite increasing public information and discussion about water supplies and growth, and their interacting consequences, there is little agreement on solutions or on the need to change life styles and expectations, particularly in those areas where water is mined from aquifers. Colorado’s Water Plan—Final 2015 (2015) attempts to answer many of these issues although its findings and recommendations are disputed by competing interests.
Forest fires: Growth in the adjacent mountains is occurring along with growth on the plains. Along with increased problems of water availability and sewage disposal (wells and septic systems are not adequate solutions in areas of higher housing density),comes the added danger of forest fires. Several large fires in recent years have burned homes and have threatened many more. Some of Colorado’s worst fires burned during the summer of 2012, including the Lower North Fork (southwest of Denver), High Park (west of Fort Collins), and Waldo Canyon (Colorado Springs) fires. Major fires affected the westernmost Front Range suburbs during the summers of 2000 and 2002. Fires have occurred along the mountain front traversed in this trip (Rocky Flats and North Table Mountain), but as grass re-grows in the following year, the sites of these fires are obscured. Aside from the immediate dangers from burning, the burned over areas become subject to flash flooding and mudflows due to incineration of the ground cover (Fig. 3). The mud and other debris washing into streams affect the fishery and contribute to the premature filling of water-storage reservoirs.
Oil and gas versus housing development is a serious issue along the Front Range corridor north of Denver as housing development encroaches into the greater Wattenburg gas field and overlying oil fields in the Denver Basin. Although active drilling has been occurring in the Denver Basin since the 1950s, only in the past 10-15 years has significant housing development moved into the actively drilled areas.3
One of Colorado’s oldest continuously operating oil fields is the Boulder Field, which is located around the intersection of the Diagonal Highway and Foothills Parkway in northeast Boulder. It was only recently plugged and abandoned.
The September 2013 floods in Colorado resulted in the release of 48,250 gallons of oil and 43,479 gallons of produced oil-field water, and an estimated 200 million gallons of untreated sewage (COGCC, 2013; Hoyt and Jar-rett, 2014). The release of the oil and produced water was viewed by many as a more serious environmental consequence than the release of the raw and partially treated sewage, even though the incidence of E. coli contamination was a far more serious public health hazard (Denver Post, 8 October 2013). This is an example of public ignorance being aroused by those with an anti-petroleum development agenda.
STOP 1: Coal-Mine Subsidence and Fire, Marshall
0.16 km (0.1 m) north of the zero point at Cherryvale and Marshall (Hwy. 170) Roads at (39° 57.29’ N, 105° 13.40 W).
Marshall is the westernmost of a series of towns located along the Boulder-Weld coal field. These towns include Superior, Louisville, and Erie. Originally, these were coal mining towns rather than their current status as bedroom communities and, more recently, sites for various high-tech companies. Mernitz (1971) describes the history of Marshall and the environmental impacts of coal mining on the area. The coal occurs in several seams throughout the Laramie Formation. The coal mine fires, which reportedly started in the 1870s (Mernitz, 1971), are gradually burning out. In 1967, it was possible to smell the coal fires on a calm day along Marshall Road (Abbott’s first visit to the area). Mernitz (1971) detected subtle evidence of continued burning in color infrared photographs.
The subsidence pattern in the open-space area to the northeast of the intersection of Marshall and Cherryvale Roads reflects the room-and-pillar-mining pattern of the underground workings directly below (Fig. 4). The mine depth here is roughly 9-12 m (30-40 ft) and the coal seam was 1.5-1.8 m (5-6 ft) thick. The piston-like nature of the sinkholes (depressions) reflects the very brittle, low tensile strength sandstone beds that overlie the coal (Fig. 5). Walking across the area on a chilly day, it is possible to detect steam and coal-gas vapors caused by a smoldering fire under this area. The irrigation ditch on the hillside has undergone significant structural strengthening through this section to maintain proper flowing grade.
The coal-mine fire and related subsidence have imposed considerable land-use constraints on the Marshall area. Houses have to be sited on a lot-by-lot basis, based on carefully locating unmined pillars and the limits of mining. Boulder County has acquired a good deal of land in the area for open space, thus avoiding future development problems. Significant areas of subsidence due to coal mining can be seen south of Marshall Road between Cherryvale Road and the hamlet of Marshall.
Although mine fires are not a problem elsewhere in the Boulder-Weld coal field, subsidence problems exist in other areas. Louisville has been the site of extensive, detailed study (see the cover of Creath, 1996). Coal-mine fires occur in other parts of Colorado. Stressed vegetation and the lack of snow cover in the winter mark some of the fires in seams south of the Colorado River between Glenwood Springs and Newcastle in western Colorado. One of these seams initiated the Coal Seam fire of 2002, which burned some homes on the western edge of Glenwood Springs. The brick-red color of coal-fire clinker (the baked rocks overlying the coal; the color is due to the oxidation of iron) is visible near Walsenburg in southern Colorado and in the eastern Powder River Basin in northeastern Wyoming.
Discussion—Natural Resources and Electric Power
Coal-fired power plants have traditionally been one of the chief sources of electric power in Colorado and the United States. Colorado continues to mine and use substantial amounts of coal. Several coal trains, each carrying 100,000-110,000 tons, go through Denver every day. Coal only occurs in some locations, locations that may be valued for other reasons as well. Mining, particularly strip mining, disturbs the land.
But we all use electricity. The Wall StreetJournal reported 14 years ago that our increasing use of computers and related technology is causing significant increases in the per capita consumption of electricity. Today’s college students have computers, printers, TVs, phones, small refrigerators, tablets, and microwaves in their rooms. Not so long ago, an electric typewriter, clock radio, and stereo set constituted the major electrical appliances in dorm rooms.
People want the electricity. The cost per kilowatt for coal-fired electric generation is half of that for natural gas. Electricity from other sources is even more expensive (unsubsidized). But many people don’t want coal mining, nuclear power, oil and gas drilling, or hydroelectric dams. Solar and wind power are not sufficient to meet our base-load demands for electricity and cost more per kilowatt hour. The increased cost of alternative energy adversely directly impacts the economically disadvantaged, a fact regularly ignored by alternative energy advocates. Is ignoring the increased energy cost ethically or morally correct? And do you really want to live next to a wind farm? Hydrogen fuel cells consume more energy than they produce in order to generate the hydrogen. We can’t have all our wants. What will each of us individually, and collectively, do?
Directions to Stop 2at N 39° 54.00, W 105° 14.49: Exit the trailhead parking area and turn left to the intersection with CO Hwy. 93 (stoplight). Turn left (south) on CO Hwy. 93 (to Golden). Continue on CO-Hwy. 93 for 6.2 km (3.8 mi) to the parking lot on the right for the Rocky Flats Lounge; proceed to the south end of the lot. This is Stop 2.
Roll-By Points of Interest between Stops 1 and 2
Coal Creek crossing: South of the intersection with CO Hwy. 128—west 120th Avenue—CO Hwy. 93 crosses Coal Creek. This is where Coal Creek flows northeast towards Superior, Louisville, and the Flatirons Crossing mall. You’ll hear more about Coal Creek at Stop 3.
Lightweight aggregate quarry: Just south of the Jefferson County line near the crest of a hill, we will cross over the conveyor belt for the shale expanded aggregate quarry to the west. On the east side of the road is the plant and kiln used to create the expanded aggregate. Prepare to turn right for Stop 2 in 0.9 km (0.6 mi). The quarry, which is well hidden from the road, is immediately behind you to the right (west).
STOP 2: Rock and Aggregate Quarries, North Rocky Flats
N 39° 54.00, W105° 14.49’; 7.08 km (4.4 mi) from zero point.
When crossing the county line from Boulder County to Jefferson County, you will notice an increase in mining and industrial activities. On the right (west) side of Hwy. 93 is the TXI shale-mining operation. The pit is ~100 m deep and provides good exposure of the Pierre Shale, as well as an opportunity for fossil collecting (e.g., Cretaceous Baculites and other marine fossils). The Pierre Shale is mined and processed into a lightweight aggregate. Across the highway (east side), the shale is “baked” in a rotating kiln (Fig. 6) into a hard, light aggregate that is primarily used in the construction of buildings where the weight of concrete is an important consideration. The processed fine-sized material is also used as an alternative to sand on area roads during the winter. These materials create less dust than sand, and help to mitigate some of Denver’s PM10 air-quality index concerns.4
PM10 is a particulate matter index referring to particles less than 10 microns in size that is used by the Environmental Protection Agency as one of the measures of air quality. Particulates can be either solids or liquid drops. Dirty air is caused by particulates more than most polluting gases, which are generally colorless.
Rocky Flats is a major geomorphic surface in the metro area. It is the oldest and highest erosional pediment in the area. It is rocky in part because of occasional extreme winds. CO Hwy. 93 is often closed to at least some types of vehicles due to high winds, especially in the spring and fall and when a good Chinook wind gets going in the winter.
Just south of the shale-processing plant, the Rocky Flats Alluvium is mined for construction aggregate. The clays of the Laramie Formation are also mined for local brick production.
Looking again toward the mountains (west), we see a pronounced red scar along the base of the flatirons on Eldorado Mountain, ~3.2 km (2 mi) away. This is the Eldorado Canyon quarry, which produced construction aggregate from the Lyons Sandstone. In the mid-1980s, due to lack of support from Boulder County residents, an application to expand the quarry was defeated. Boulder County Open Space has since purchased the site and attempted to reclaim it. The long tan scars across the lower flank of the mountain are clay mines in the Dakota Group. The refractory-grade, kaolinite-rich clay is used for industrial ceramics and bricks. Although these clay pits usually look abandoned, many of them are active mining sites. But they are not mined on a daily basis. Mining only occurs when a supply of the particular clay in a quarry is needed. Clays vary in color and chemical quality, either or both of which may be needed for particular applications.
Quarries can be noisy, dusty, and ugly. But we want what comes out of them, the raw materials for bricks and concrete, for landscaping rock, for road and trails, for building stones, for clay and ceramic products, and kitty litter. Why is someone else’s backyard a more appropriate location than yours? Some former aggregate quarries are now the ponds full of plants and wildlife lining the Platte River greenway, the area north of Chatfield Dam and C-470. Today’s eyesore can be tomorrow’s benefit (Figs. 7, 8, and 9).
Directions to Stop 3:Turn right (south) on CO Hwy. 93 and proceed 3.7 km (2.3 mi) to the intersection with CO Hwy. 72. Turn right (west) toward Coal Creek Canyon. After 2.7 km (1.7 mi), turn right on Plainview Road. Drive 0.3 km (0.2 mi) and pull over onto the right edge of the road. This is Stop 3 (N 39° 52.55, W105° 16.16).
Roll-By Points of Interest between Stops 2 and 3
Leyden Gulch: As we approach Stop 3, driving toward the mountains on CO Hwy. 72, look to the left at the developing head of Leyden Gulch, which will be a topic of later discussion. Also, look across the gulch to the railroad track to the tan railroad cars parked along a curve in the track (Fig. 10). These cars are permanently in place and are filled with rock. They provide a wind barrier to prevent empty cars on passing trains from being blown off the track. The Rocky Flats area is infamous for high winds. These result from the fact that the low point in the Front Range on the east end of the Colorado River on the western slope is west of Coal Creek Canyon. Wind, like water, flows through low points.
The Moffat Road is the main rail line heading west from Denver and is known to most native Denverites as the route of the ski train to Winter Park.
STOP 3: Canyon Flash Flooding, Coal Creek Canyon
N 39° 52.55, W105° 16.16; 13.84 km (8.6 mi) from zero point.
All larger drainages along the Front Range head in the mountains and fall rapidly from alpine elevations (above 2900 m or 9500 ft) through steep-gradient canyons. These debouch at the mountain front onto the piedmont, where stream gradients lessen substantially. There is typically 1830-2590 m (6000-8500 ft) of relief from the highest mountain summits to the highest parts of the piedmont. The resulting orographic and meteorological effects on streamflow can be pronounced and extreme.
At this locality near the mouth of Coal Creek Canyon, we can see a sequence of flood deposits produced by events similar to the 1976 Big Thompson Flood or the fall 2013 floods. The Colorado Geological Survey) obtained a 14C date from this locality of 955 ± 80 yr B.P. from what were interpreted to be the youngest of three flood deposits. CGS 14C dates from similar materials at other Front Range localities range from ~10,000 yr B.P. to 300 yr B.P.
A major historical flood along the Colorado Front Range occurred in the drainage of the Big Thompson River, Larimer County, during the night of 31 July-1 August 1976. This flood can be attributed to one thunderstorm event when a large cell remained nearly stationary over the middle part of the drainage basin for ~2.5 h. Nearly all of the tributary streams in this part of the basin were involved. East of Drake, relatively little rain fell during the event. A peak discharge of the Big Thompson River of ~39,000 cubic feet per second (cfs) was computed at the mountain front, ~4 mi west of Loveland. An estimated 139 people were killed during this event and property loss of about $40 million (1976 dollars) resulted. Overbank flooding downstream from the mountain front occurred through the City of Loveland to the river’s confluence with the South Platte River. The Colorado and U.S. Geological Surveys documented the geomorphic effects of this event (Soule et al., 1976; USGS, 1979). These included debris avalanches and flows, deep scour of ephemeral stream-beds, deep sheet erosion on hill slopes, and deposition of prodigious amounts of sediment on gentler slopes above normally active stream channels and on the river’s piedmont floodplain. Clearly, being above the high water mark in the channel is not equivalent to safety for either people or structures.
The floods along the Front Range in September 2013 caused even greater damage, not only in the Big Thompson Canyon, but also along a number of other streams including the North and South St. Vrain Creeks, James Creek, and others and eventually along the South Platte River into which all of these streams drain. Over 486 miles of road were destroyed and 102 bridges were washed out or damaged. There were 24 affected counties. There was an estimated $3.5 million (in 2013 dollars) in crop losses and interruption of 225 water diversions, primarily for irrigation ditches. About 200 million gallons of raw sewage were released and 14 oil and gas operations had “significant spills,” which released 48,250 gallons of oil and formation water. About 19,000 homes were damaged (1500+ destroyed) and 11,000 people were displaced. The 2013 storm occurred over several days of extremely heavy and steady rain that soaked the soil. Soaked soil is far more erodible than the dry soils affected by the 1976 flood. The 2013 floods also triggered a large number of debris flows on the hillsides above the streams. The recurrence interval is estimated at 1/500-1/1000 in some locations (Hoyt and Jarrett, 2014).
Flood events of similar or possibly less magnitude have undoubtedly occurred in many Front Range drainages during the Holocene. Soule, Costa, and Jarrett studied paleoflood deposits in 14 drainages along the Front Range during the late 1970s and early 1980s (Hoyt and Jarrett, 2014). This was done to support a broad research proposal to model Front Range paleofloods and modern floods. The study was never completed because of “fiscal malnutrition.” Evidence for these occurrences includes geomorphology of paleoflood deposits, discharge estimates based on flows necessary to move largest clasts (boulders) entrained in paleoflood deposits, depth of scour in streambeds, superposition of streamflows in channels, 14C dating, study of demonstrable glacier-related deposits, and meteorological computations. Jarrett (1987) offered field evidence for and proposed that the Big Thompson event has a recurrence interval of 10,000 years, and that storms of the magnitude to produce such an event must form below 2600 m (8500 ft) in altitude. Some debate about this continues, however. Flooding in the Black Hills drainages has recurrence intervals in hundreds of years (Perry Rahn, 2012, personal commun.). The Black Hills floods are surrounded by the Mad-dison Formation, which has lots of caves that trap flood flotsam at various levels and that provide better dating precision than provided by the Colorado floods. The 37-yr period between the 1976 and 2013 floods on the Big Thompson River suggests that the Black Hills recurrence interval estimates may be more accurate.
Later in the trip, we will be crossing several of these streams: Ralston Creek, Van Biber Creek (Stop 4), Clear Creek, Mt. Vernon Creek, Bear Creek, and Turkey Creek. Ralston Creek is the only one with a dam upstream of where we will cross. Clear Creek has no flood control dams. The Bear Creek dam is well east of the Dakota hogback at Morrison, leaving the town of Morrison unprotected from floods along Mt. Vernon Creek and Bear Creek; both streams have flooded Morrison within the lifetimes of some of the people on this trip. In 1969, Turkey Creek flooded and eroded out all four lanes of U.S.-285 a few miles west of the mountain front in one place, and two lanes for a good portion of the distance between Tiny Town and the mountain front near The Fort Restaurant. In June 1965, the Plum Creek-South Platte flood washed out I-25 at Castle Rock and collapsed or damaged most of the bridges south of Colfax Avenue. Although Chatfield Dam was built to prevent similar flooding in the Denver area, the areas upstream of Chatfield Dam remain unprotected and vulnerable.
Even very small drainages can flood and cause damage. In June 2004, a number of small storms around Golden precipitated 5-7 cm (2-3 in) of rain in short periods of time. One small drainage in north Golden flooded and destroyed one home built on the lower part of what was probably viewed as an insignificant gully. Significant amounts of mud and sand were deposited on Golden streets prior to reaching Clear Creek. Significant erosion also occurred in part of the Van Biber Creek channel (Stop 4).
The valley to the south of CO Hwy. 72 (up which we drive) is the headwaters area for Leyden Gulch (Fig. 11). It is a fairly prominent valley that parallels the pronounced break in slope at the base of the foothills. The upper end of the gulch contains a steep channel that has eroded to within 1.2 km (0.75 mi) of the main channel of Coal Creek. It has migrated between 61 and 76 m (200 and 250 ft) northward in the past 30 years. Examination of the head of Leyden Gulch on Google Earth in photos taken between 4 October 1999 and 18 August 2011 shows Ley-den Gulch deepening and extending westward. If this rate of advance continues, it is logical to expect that Leyden Creek will capture the upper (mountain) part of Coal Creek, an event known as stream piracy or stream capture.
Discussion—Flooding and Development
If a flood like the 1976 flood on the Big Thompson or a locally more severe version of the 2013 flood event were to come down Coal Creek, the large boulders and other debris carried within the mountain canyon would drop out of the stream after the stream exits the mountain front. This would tend to block the channel and cause water to spread out. If some of this water spread into Leyden Gulch, the stream capture process could take place rather rapidly (tens of minutes to a few hours?). If this were to occur, western Arvada would face an unplanned-for flood threat. If Coal Creek were not captured by Leyden Creek, flood damage to newly developed areas downstream on Coal Creek, especially near Superior and Louisville, could be significant.
Flood control dams are not popular with those favoring open rivers. They also do not protect those upstream from the dams. Furthermore, dams have been known to fail. Even small dam breaks can generate catastrophic results, for example, the Lawn Lake Dam failure in Rocky Mountain National Park that swept through Estes Park in 1982.
Even downstream of dams, developing housing in an area results in significant increases in surface runoff because roofs, driveways, walks, etc., are impermeable. They cannot absorb water and slow it down. As an area is converted from pasture or farmland to urban houses and shops, the size and suddenness of flash flooding from the same-sized rainstorm can increase. As the small but high intensity storms in Golden in June 2004 demonstrated, even very small drainage basins can flood and cause significant damage to property.
Directions to Stop 4at (N 39° 46.00, W 105° 13.67): Turn around and return to CO Hwy. 72. Turn left (east) and go to CO Hwy. 93, then turn right (south) toward Golden. Once in Golden, turn left at the third stoplight onto Iowa Street.The service stationjust off Hwy. 93 and Iowa is a good place for a rest stop.Go three blocks on Iowa Street to the stop sign at Ford Street. Turn right on Ford Street and then almost immediately turn left into the parking lot of the Hillside Community Church. The lower parking lot on the east (far) side of the church is Stop 4.
Roll-By Points of Interest between Stops 3 and 4
Devils Backbone, clay pits, and gas and storage: Descending into Leyden Gulch on CO Hwy. 93, we will travel along the base of a near-vertical exposure of lower Laramie Formation sandstone (locally known as the “Devils Backbone”). Between these vertical sandstone ribs are the collapsed stopes of old, abandoned clay and coal mines and uranium prospects (Fig. 12). Coal was also mined east of the “Devils Backbone” in the Leyden mines described in the following discussion point on the former gas-storage, now water-storage facility.
Discussion Points—Natural Gas Supplies for Urban Areas
Keeping a supply of natural gas near urban areas is a continual problem for utility companies. These supplies are required to meet surges in demand during winter cold snaps and other events. On the east side of the Devils Backbone hogback, down Leyden Gulch, is the site of the former Leyden coal mine gas-storage facility, formerly used to store 3.5 billion cubic feet of gas in an old coal mine. This facility was decommissioned following the discovery of leaking gas. Prior to the installation of the Leyden mine facility, Public Service Company of Colorado, now part of Xcel Energy, used storage tanks like that pictured (Fig. 13) for urban supplies. One of these tanks was located about a block from a junior high school. Clearly, this is not the type of facility that could be approved for construction in a developed area today. The Leyden facility replaced such storage tanks in the Denver metro area.
Closure of the Leyden facility resulted in new techniques to provide the required surge-gas storage capacity. These techniques include the use of larger diameter, high-pressure mains and storage in abandoned gas reservoirs at distances not too far from the Front Range corridor. We are fortunate that the local geology contains such reservoirs in the Denver Basin. This would not work in other parts of the country such as New England. However, as demonstrated by the events in Hutchinson, Kansas, on and following 17 January 2001, where a sudden release of gas resulted in the destruction by fire of a number of businesses, using old fields for storage is not without problems. M. Lee Allison (2001), former Kansas State Geologist, provided an excellent summary of the events in Hutchinson.
The old Leyden mine has been converted into a water storage facility. Underground water storage has the advantage of not being subject to evaporation losses. Because the coal extracted from the Leyden mine was low in sulfur, acid resulting from oxidation of pyrite is not expected to be a problem with this facility. Figure 8 shows another example of a mine (quarry) being converted to water storage.
North Table Mountain: As we approach the town of Golden on CO Hwy. 93, North Table Mountain comes into view. Both North and South Table Mountains are basalt capped. The underlying sedimentary rocks are nearly flat-lying and range in age from Cretaceous through Tertiary. The famous K-T boundary, the extinction event marking the end of the dinosaurs (except the birds), can be located on the slopes of North and South Table Mountains.5
Some controversy exists about whether the K-T boundary, which is marked by impact debris and anomalously high iridium values, caused or merely coincided with the mass extinction at the end of the Cretaceous. Most current evidence suggests the events coincided, but this is not quite the same as cause.
Clay pits in the Dakota hogback: As you proceed south, clay pits, visible as faces of shear, tan- or buff-colored rock, which occur along the Dakota hogback, can be seen on the right. The prominent, planar surfaces of tan-colored rock are bedding planes in the Dakota Sandstone, which dip steeply east. The clay-pit stopes also follow the bedding planes, and were typically dug downward until the water table was encountered. As noted about the pit pictured in Figure 7, while many of these clay pits appear to be abandoned, they are not. They are mined as the brick and other companies that own them need more of the clays found within particular pits.
Most older buildings and homes in Denver are built of brick in order to (1) avoid the catastrophic fires that plagued so many cities in the nineteenth century, and (2) because brick was cheaper than lumber. Clays are also the basic constituent of all sorts of ceramic products like tiles; clay for pots, cups, and plates; and high-temperature furnace linings, insulators, crucibles, pipes, etc.
Approaching Golden—Possible C-470 Corridor: The housing developments in the Ralston Creek valley and the expansion of Golden north of North Table Mountain create a major NIMBY (“Not In My Back Yard”) obstacle to what would otherwise be a good route for extending C-470 around the northwest quadrant of the metropolitan area. C-470 now connects directly to west 6th Avenue/US-6 and thus into CO Hwy. 93 going north to Boulder. Had the C-470 route been designated prior to the construction of these homes, the NIMBY factor would have been avoided. The City of Golden is asking that C-470 be dug underneath Golden to avoid disturbance of any neighborhoods or that C-470 be routed east of North and South Table Mountains (and disturb someone else’s neighborhood). Given that CO Hwy. 93 is the main connection between Boulder and US-6 and I-70 going west into the mountains, it may seem a little surprising that CO Hwy. 93 remains essentially a two-lane road.
STOP 4: Rockfall and Landslides, North Table Mountain, Golden
N 39° 46.00, W105° 13.67; 29.8 km (18.5 mi) from zero point.
The rockfall- and landslide-hazard area around North Table Mountain was mapped by the U.S. Geological Survey during the 1970s (Simpson, 1973a, 1973b). Jefferson County has adopted the mapped hazard area as part of its geologic-hazards overlay, and has considered it to be a “no-build” area. This was challenged in the 1980s by a developer, who staged an actual rock-rolling demonstration on the northwest flank of the mountain in order to prove the fallacy of the outer (distal) hazard-area boundaries. The demonstration was curtailed (and the subdivision application was subsequently denied) after several boulders rolled beyond the outer boundary, but not before one boulder had bounced at least 3 m (10 ft) into the air and knocked a cross-bar off a high-tension power-line tower at the base of the mountain (Jeff Hynes, test witness, 1999, personal commun.).
The rockfall- and landslide-hazard areas, as mapped by the USGS, exist in both unincorporated Jefferson County and the incorporated City of Golden. Unfortunately, protection of the public from these hazards does appear to stop at the jurisdictional boundary in this case (Fig. 14). The houses we see on the hillside above are located within the City of Golden, which has not adopted the maps of Simpson (1973a, 1973b). This subdivision was approved and built due the absence of any requirements for home-rule cities to follow the state-mandated, geologic-hazard review process for these subdivisions.
Building continues in this area of Golden. Figure 15 is a photo of a “lots available” sign that was taken in late May 2004 along Cliff Line Road in Golden. The available lots were above existing homes. Figure 16 shows Dave Noe standing on the rocks excavated from a house under construction along Cliff Line Road above existing homes in late May 2004.
Discussion—Rockfalls and Landslides
Rockfall and landslide hazards are common in Colorado. Any area with cliffs and steep hillsides may have rockfall potential. The rimrock areas of Douglas County are subject to rock falls, landslides, and debris flows. Some scars from the 1965 Plum Creek-South Platte River flood are still visible on the south side of Hunt Mountain, a prominent mesa south of Castle Rock. Think about rockfalls the next time you drive through the Vail Valley. There are some fascinating debris flow, mudflow, and landslide features in the Vail area as well.
Landslides on steep slopes can be a significant hazard. The destruction of several homes in one of the subdivisions on the north side of Green Mountain starting in 1998 is but one example. The existence of the landslides had been geologically mapped prior to development. The developer’s geologic consultant recommended remedial actions that were subsequently ignored.
Several of the references listed at the back of this road log are maps published by the Colorado Geological Survey and the U.S. Geological Survey showing geologic hazards in various parts of the Denver metro area. Similar maps are available for other areas.
Why isn’t there stronger geologic hazard zoning? Well, who is going to pay landowners for their lost property values? Think about how you would feel if your family ranch was put off-limits to development rather than providing the money for your children’s and grandchildren’s education. Somebody will suffer economic loss, individuals or taxpayers or both. The political debate involves who, and how much.
In Memory of a Former Stop: Differential Clay-Pit Compaction and Expansive Soils—CSM Married Housing
Earlier versions of this trip stopped in the married student housing area of the Colorado School of Mines (CSM). After many years, the damaged buildings featured at this former stop have been torn down and new buildings built. But we still have pictures that document what happened and so have left the relevant text in this field guide for your consideration.
This former stop looked at the challenges of multiple-sequential land use as related to clay mining operations and reclamation along the western side of Golden. Here, an array of open-stope clay pits along the east side of U.S. Highway 6 have been reclaimed for several uses with a variety of problems and solutions, some more successful than others.
Severe differential-settlement problems were experienced in the student housing at Colorado School of Mines, along Campus Road (Figs. 17 and 18). The fill used to reclaim this area settled, perhaps only a few percent, but the bounding sandstone ribs were and are stable. Major differential settlement and damage has occurred where structures, flatwork, and roadways straddled these highly variable units.
South of the CSM campus, the clay pits were simultaneously used as landfills and to dispose of fly ash from power plants. Unresolved water-quality issues led to the termination of this program, and the remaining reclamation is being performed with unregulated materials such as random fill. This may prove to be a future land-use issue for the City of Golden.
Some of these pits were incorporated into the Fossil Trace Golf Course. In some of the upper Cretaceous sandstone exposures, dinosaur tracks are visible. The development of this golf course provoked some controversy over the number of trackways that would be preserved, and the amount of public access that would be available for those wishing to visit them without playing golf. Agreement to allow public access to the trackways and the construction of bike paths resolved the controversy.
There are many reclaimed dumps—the older word for landfill—around the Denver area. Cherry Creek Shopping Center sits on one. The site of the original Mile High Stadium (demolished) and Sports Authority Field at Mile High occupies an old Denver city dump.6
Sports Authority declared bankruptcy in March 2016 and whether the Sports Authority name will remain on the stadium after August 2016 was unknown at the time this road log was revised.
Expansive soils are a problem throughout much of the metro area. These are due to the presence of certain clay minerals, particularly bentonite,7
Bentonite is an older, but common term for swelling clays that are now recognized as mixed layers of illite and smectite formed when volcanic ash falls into lakes or oceans. Charge imbalances in the clay mineral structure allow water to be absorbed into the mineral structure, causing the swelling that creates the problems for foundations. Different bentonitic layers have differing characteristics. “Bentonite” is still used for the clays in such industrial mineral products as drilling mud, foundry casting binders, and kitty litter.
In recent years, development along the hogbacks has revealed a whole new set of swelling clay problems where the clays are steeply dipping. The standard methods of drilling in order to test soils failed to alert developers to the problem—someone ignored the well-known geologic character of the mountain front. Again, the result is homes with significant structural damage (Figs. 19 and 20).
As with the rockfall and landslide hazards discussed earlier, geologists were aware that the sedimentary layers were turned on end near the mountain front. But that information was not effectively communicated to developers and land-use planning agencies in a way that required action to account for differences in geology. The geologic information was ignored. To what degree is this failure to communicate the geologic profession’s problem, and to what degree is the problem of those who don’t view geology as important or worth the bother? The result is economic losses for homeowners, developers, government agencies (the Jefferson County Public Schools had to condemn and demolish an elementary school), and taxpayers. The Colorado Geological Survey has published a popular disclosure booklet for expansive soils (Noe et al., 2007), targeted at builders, homebuyers, and homeowners; over 300,000 copies have been distributed.
Directions to Stop 5, Red Rocks Amphitheatreat (N 39° 39.98’, W105° 12.45’): Exit the church parking lot by turning left (south) on Ford Street. Proceed downhill 1.1 km (0.7 mi) to 10th Street and turn right. Go two blocks to Washington Avenue.(Note: the field-trip lunch stop will be at Parfet Park, located at 10th Street and Jackson, one block west of Ford.)Turn left on Washington Avenue. Cross Clear Creek, and continue through downtown Golden and up over a hill to 19th Street, turn right on 19th Street. At 6th Avenue (US-6) turn left (south or east, depending on how you look at it). After 2.1 km (1.3 mi), turn right at the light onto Heritage Road (CO Hwy. 93). In 1.6 km (1 mi), merge on to US-40 going south (or west) and continue under 1-70, where the road designation changes from US-40 back to CO Hwy. 93, and continue going south toward Red Rocks Park and Morrison. After 2.3 km (1.4 mi), turn right into Red Rocks Park (gate 1). Follow the main road 2.4 km (1.5 mi) to the top of the amphitheater. This is Stop 5.
Roll-By Points of Interest between Stops 4 and 5
Clay pits along 6th Avenue: As you travel along 6th Avenue, there are various clay pits on the left in various states of being filled. One hopes that the lessons of CSM’s experience with student housing have been learned here. The new Fossil Trace Golf Course occupies some of these pits.
I-70 roadcut—Point of geologic interest: There are walkways along both sides of I-70 as it crosses the Dakota hogback, which allow detailed examination of the exposed Upper Jurassic Morrison and Cretaceous Dakota Formations. LeRoy and Weimer (1971) published a detailed guide to both sides of the cut with pictures and detailed stratigraphic sections. Unfortunately, weathering and erosion in the 45+ years since the cut was first made obscure some of the detailed features of the stratigraphy. The Morrison Formation on the west side of the cut is variegated reds and greens in color and consists of sandstones and mud-stones. It is the classic “Jurassic Park,” from which skeletons of many well-known dinosaurs have been excavated around Colorado, Wyoming, and Utah. It was originally described at and named for the town of Morrison, where some of the earliest excavations were made by Arthur Lakes. The Morrison Formation and the Dakota Sandstone will be discussed in more detail at Stop 5.
Mt. Vernon Creek floods: After passing under I-70, the road follows Mt. Vernon Creek down to Morrison. Going upstream, Mt. Vernon Creek turns west and is followed by I-70 to the Genesee divide. While Mt. Vernon Creek is normally practically dry, it can flood. When it does, downtown Morrison could be in trouble. Water has flowed through the buildings in downtown Morrison in the past, and the increased construction of homes in Mt. Vernon Canyon is probably exacerbating the flood problem by creating large, impermeable areas.
Alameda roadcut and Red Rocks Park: The Alameda road-cut and the north entrance to Red Rocks Park intersect CO Hwy. 93 about 2.3 km (1.4 mi) south of I-70. The Alameda roadcut goes through the crest of Dinosaur Ridge, the name for this part of the Dakota (Formation) hogback, a very worthwhile stop of C-470 on the east side of the hogback for those interested in dinosaurs. Red Rocks Park features some geologic exhibits and is an excellent place to examine some of the features of the mountain front.
STOP 5: Bringing Geology to the Public, Red Rocks Amphitheatre
N 39° 39.98, W105° 12.45; 43.6 km (27.1 mi) from zero point; the parking lot for the amphitheater.
The Red Rocks Amphitheatre is a place where many Coloradoans and visitors become aware of geology. The site is a marvel of natural rock formations, hewn stone, concrete, and wood (Fig. 21). Remnant hogbacks of the red Pennsylvanian-Permian Fountain Formation flank the seating areas and, along with the panoramic view of the Denver area, provide a dramatic backdrop for the stage. Built by 200 men from the Civilian Conservation Corps (CCC) and opened in 1941, the amphitheater is a tremendously popular attraction. It is visited by 750,000 people per year, including 350,000 who attend concerts given by national and international musicians. The Easter sunrise service is a long-time favorite event for many Colorado families.
The amphitheater has recently undergone a major renovation to improve the facilities and infrastructure, and to repair damage that has occurred over the years. In particular, the southeast part of the seating area was undergoing movement, deformation, and cracking. Was the amphitheater built on a landslide? Investigations by the Colorado Geological Survey and private geotechnical firms determined that the damage was being caused by settlement and movement of fill, which was found to have been dumped into place as uncompacted fill by the CCC during construction (Dodson et al., 2003). Poor storm drainage had contributed to the problem, and large void areas had formed beneath the seats due to erosion and transport of the granular fill material. The area was remediated using compaction grouting, reinforced-soil slopes, and ground anchors. Lightweight, concrete flow fill was pumped beneath the seats to fill the eroded voids.
Two of the more challenging aspects of the renovation are the site’s historic designation, which required every removed item to be cataloged and reinstalled in its original position, and the need to design the improvements in harmony with the terrain and landscape. One of the highlights is a new, underground visitor center at the top of the amphitheater. The geologic constraints of this particular site necessitated the use of soil-nail walls and mechanically stabilized earth walls up to 10.7 m (35 ft) high. The design has been form-fitted into the existing geology, exposing large boulders. The new visitor center includes a display of the geologic evolution of Red Rocks Park.
Discussion—Geology and Public Education
Over the years, the Rocky Mountain Association of Geologists has constructed a number of signs identifying formations and other explanatory plaques on the geologic feature of Red Rocks Park. In the past few years, the Friends of Dinosaur Ridge have done a great deal of work preserving, making accessible, and providing explanations of Dinosaur Ridge along the Dakota hogback immediately east of Red Rocks Park. The top of the hogback is formed by the east-dipping sandstones of the Dakota Formation. Below the Dakota Formation and forming most of the slope of the hogback visible from the amphitheater is the Morrison Formation, the original Jurassic Park and location of many dinosaur quarries around the western United States. Some of the first dinosaur excavations were near the town of Morrison. These are commendable efforts in public education.
Natural history museums also assist in public education. However, museums tend to focus on mineral collections and fossil displays, which, while part of geoscience, are still only a small part of a broad field. Most geologists are neither mineralogists nor paleontologists, even though we know something of these subjects and may use them regularly. Do such exhibits contribute to the view expressed by some that geology is a form of stamp collecting?
How can we, as geoscientists, teach the public about broader aspects of geology? Trips like this are one method, but one which does not address the whole of the field either. Many of us became geologists because we took Geology 101, for whatever reason, and realized what a varied and fascinating field it is. John McPhee’s books, assembled in Annals of the Former World (1998), provide a sense of the coverage of the field and some of the things that geoscien-tists do. Again, think about how each of us can contribute to a broader understanding and appreciation of the variety of things that we collectively do for a living and that provide vital information and resources for society as a whole.
Directions to Stop 6at (N 39° 38.108, W105° 10.106’): Turn around and drive out of Red Rocks Park, then turn right (south) on CO Hwy. 93. When you reach the junction of CO Hwy. 8 in downtown Morrison, turn right (west). Turn south at the second stoplight, following the sign to US-285 and crossing Bear Creek. Proceed south 2.6 km (1.6 mi) and turn left on Turkey Creek Road (at N 39° 37.88, W105° 11.59). Proceed east for 2.6 km (1.6 mi) (watch for the sharp turn taking you under US-285) to where you can pull off on the right side of the road near the far (east) end of the cut in the Dakota hogback. This is Stop 6.
Roll-By Points of Interest between Stops 5 and 6
Driving south from the town of Morrison, notice the lack of the type of suburban development observed along US-36 between Denver and Marshall. Lack of available water taps is part of the reason. Further south (south of the US-285 freeway and Turkey Creek) suburban development begins again.
At 1.9 km (1.2 mi) south of Morrison is the access to Aggregate Industries Morrison quarry. Although not much more than the upper part of the crushing plant is visible from the road (Fig. 22), the pit that will be turned into a water reservoir for Morrison was taken in part of this quarry. This quarry has won various environmental awards for shielding its operations from view and for reclaiming those high walls that can be seen from Denver.
STOP 6: Oil Reservoir and Uranium Deposit, Turkey Creek Gap
N 39° 38.108, W105° 10.106; 57.1 km (35.5 mi) from zero point.
Stop hazards: Rocks can fall from the cliffs at this stop and the traffic along Turkey Creek frontage road can move at high speeds. Stay back from the cliffs and off the black top.
Oil deposit: The tan sands at the top of the Dakota Formation contain a “fossil” oil deposit that can be seen as a distinct color change to a more greenish-gray color; see Figure 23. The oil deposit is “fossil” because all of the lighter hydrocarbons have evaporated off, leaving only the heavy, asphaltic components. If you smell one of the oil-bearing rocks on a hot day, you may get a whiff of the oily smell. Breaking a piece of float rock open may help.
One of the main purposes of this stop is to examine what a hydrocarbon reservoir usually looks like. It is not an underground pool (there are very rare exceptions). Rather, it is a portion of a rock unit in which spaces or pores occur between the sand grains. The amount of this space, which can be filled by hydrocarbons or other fluids, is known as porosity, one of the two, million-dollar words in the petroleum business. The other million-dollar word is permeability, which describes the interconnection of the pores, allowing fluid to flow.
A kitchen sponge and a Styrofoam coffee cup illustrate porosity and permeability. Both the sponge and the coffee cup are mostly pore space; they both have extremely high porosity. In the sponge, the pores are interconnected allowing water to flow through; the sponge has very high permeability. The coffee cup has essentially the same porosity as the sponge, but the pores aren’t interconnected and the cup holds coffee. The coffee can’t leak out unless the cup is cracked (fractured).
A well-completion technique known as hydrofracing or facing (no “k”) (hydraulic fracturing) artificially improves permeability. The process consists of pumping a fluid and a propping agent like sand into the rock from the well bore with sufficient pressure to fracture the rock. The propping agent remains in the newly formed fractures to help hold them open when the pressure is reduced and the fluid is pumped back out of the rock and the well.
The Dakota Formation sandstones exposed here are known as the D-J sandstones, which are important oil and gas reservoirs in the Denver Basin of northeastern Colorado, including the Wattenburg field noted earlier in this road log.
Uranium deposit: In addition to the fossil oil, the south side of the Turkey Creek gap contains a roll-front uranium deposit. This is most clearly seen as the "C" shape of the uphill side of the top part of the oil deposit; see Figure 23. The shape reflects the cross-sectional shape of a tongue of groundwater moving through the rock. The groundwater picks up very small amounts of uranium and other elements weathering out of the mountain rocks. These elements are in an oxidized state. When the groundwater encounters reducing conditions (which can be caused by organic material like hydrocarbons) in the rocks through which the water is flowing, the uranium and other elements like molybdenum (the "moly blue," ilsemannite, a molybdenum oxide shown in Fig. 24) precipitate in a reduced state. Roll-front uranium deposits represent one of the major types of uranium deposits in Wyoming and in western Colorado, southeastern Utah, and northwestern New Mexico.
The problem with uranium deposits is the associated radiation. This is a NORM (Naturally Occurring Radioactive Material) site. An important point to remember is that radioactive elements are present throughout the environment in trace amounts. No place is radiation free.
New Hampshire is famous for its granite, and New Hampshire’s granites are relatively high in uranium and other radioactive elements like thorium and potassium (40K). People have been living in New Hampshire for over 200 years without exhibiting abnormal health problems due to radiation. This led to concluding that the background radiation amounts in New Hampshire did not cause radiation problems. Although we cannot have zero radiation risk, there has been a long-term history demonstrating that normal, background amounts of radiation do not cause an abnormal health risk.
Nevertheless, there are areas where anomalously high amounts of radiation occur. The most common radiation problem is due to radon gas. Radon detectors provide very precise measurements of radon concentration. However, because radon concentrations depend on atmospheric pressure and other weather-related phenomena, long-term measurement (several months) is required for accurate measurement of radon levels. The results from the commonly available, short-term (48 h) radon detectors will vary with atmospheric pressure, etc. If a radon problem is discovered, its solution is often not very expensive and involves providing improved ventilation of basement spaces, usually with a relatively cheap fan and PVC piping that vents to the outside. Many new homes in the Denver area have these PVC vents as standard features, because they are very low-cost construction additions.
Turkey Creek flash flooding hazard: Turkey Creek, which normally doesn’t have a particularly high flow, passes under this road and US-285 cut in a culvert. However, Turkey Creek has experienced flash flooding from time to time, and the potential exists that flood water and contained debris will cover and block US-285, perhaps even damaging it. During heavy rains in early June 2004, Turkey Creek’s flow was high enough to begin encroaching on the frontage road we’re standing next to, although the road was not blocked. In the spring of 1969, a flash flood upstream on Turkey Creek took out two of US-285’s four lanes for a good distance and all four lanes at one cutbank.
Discussion—Natural Resources Are Where They Are
We all use natural resources. Some people object to mines and oil wells. They’re not always pretty. They can be messy. Natural resources are not located in places that are always convenient. The San Juan Mountains are scenic, in part because they were formed by processes that resulted in the deposition of a variety of metals from hydrothermal deposits. In his Geo-Logic, Robert Frodeman (2003) provides an excellent discussion of the problems of acidic and metal-bearing waters in the Silverton caldera in the southwestern San Juan Mountains. The area has been actively mined, but the hydrothermal alteration and mineralization that attracted the miners preexisted mining and generated acids and released metals naturally. The catastrophic release of acid mine water from the Gold King mine during the summer of 2015 occurred just north of Silverton. Determining how much mining altered the natural system is difficult and debatable. Matt Sares (2016), formerly of the Colorado Geological Survey, has published a PowerPoint™ presentation, “Geology, Mining, and Water Quality,” that describes both naturally occurring and mine-related acid water formation. Neubert et al. (2011) is another excellent reference describing naturally occurring acid rock drainage from hydrothermally altered areas.
As this stop and the coal mines and clay quarries we’ve seen earlier show us, such deposits are where they are. If we want the products, we must exploit the resources. Even if we don’t extract them, the deposits and the processes that form and modify them continue to work. It is no surprise that Leadville and Aspen have high concentrations of lead and other metals in the soil. Mother Nature put it there. Trace elements naturally occur in our water supplies. Denver’s water is naturally high in fluorine and molybdenum, among other elements, because of the geology of the watersheds from which Denver gets its water.
Radiation occurs naturally. The amount of radiation in an area depends on the rock types present. Weathering and other geologic processes can concentrate uranium and other radioactive minerals in deposits like the one at this stop. These are the sites of greatest radiation hazard. Published uranium exploration data are available that locate potentially hazardous areas; however, this is not information readily available to (both access to the documents and text comprehendible by the layman are a problem) or consulted by land planners and developers. How should the available information and those who should be using it be brought together? The geologic information needs to be in a form the public understands, not the form of typical technical reports. Those who could benefit from using the information must be made aware that the information is available for them to use. What can we, as geoscientists, do about this?
End of trip.
Return directions:Proceed east along Turkey Creek Road to West Quincy Avenue and the intersection with E-470. Cross E-470 and turn right to E-470 north-bound. Proceed on E-470 to intersection with 1-70 eastbound. Take 1-70 eastbound to 6th Avenue; take 6th Avenue east to 1-25, then 1-25 north to Colfax Avenue (eastbound) and return to the Colorado Convention Center.
Roll-By Points of Interest Returning to the Colorado Convention Center
The route of C-470 along the east side of the Dakota hogback parallels/follows the Golden fault that thrusts Precambrian and Pennsylvanian through Cretaceous strata eastward and over the same section. The strata on the east side of C-470 are basically flat-lying Upper Cretaceous through Paleocene sediments. After crossing Bear Creek, the Bandimere Speedway complex is on the left side of the road. At Alameda Avenue, the Dinosaur Ridge Museum is on the west side of C-470, while on the east side are two clay pits actively (but not daily) being quarried for brick clay by General Shale Brick, Denver’s largest brick manufacturer. Green Mountain, a monadnock, is east of C-470 and north of Alameda Avenue.
After merging onto I-70 eastbound, South Table Mountain is visible on the left (north). The flows capping South Table Mountain noticeably thin toward the southern and eastern ends of the mountain. Clear Creek originally flowed around the south side of South Table Mountain after the eruption of the flows. Stream capture cut through the flows and separated South and North Table Mountains.
We would like to thank Jim Soule, Jeff Hynes, and Karen Berry of the Colorado Geological Survey, who wrote parts of the original manuscript (Noe et al., 1999) that was used as a basis for this paper. Dave Noe also co-lead some of the earlier versions of this field trip and provided valuable help. Marilyn Dodson of Yeh and Associates provided information about the renovation project at Red Rocks Park. Curtis L. Johnson kindly used his sources at Xcel Energy to track down Figure 13, the picture of the old gas-storage tank. Bill Hoyt and Bob Jarrett led a great field trip to areas affected by the 2013 flooding in September 2014. Charles Dimmick, Jean Neubeck, and Matt Morgan provided valuable reviews of the manuscript.
Note: In addition to the cited references, this list contains other pertinent maps and reports about the geology in the field-trip area.
Figures & Tables
Unfolding the Geology of the West
Prepared in conjunction with the 2016 GSA Annual Meeting in Denver, Colorado, this volume contains sixteen guides to field trips in this rich geologic region. The four “Great Surveys” of the late 1800s ventured west to explore and document the region’s unknown natural resources and collect valuable geologic information. Many of the field guides in this volume, aptly titled Unfolding the Geology of the West, will cover the same hallowed ground as the early geologic expeditions. Organized into four sections, this volume spans some of the major subdisciplines of geology: (1) stratigraphy, sedimentology, and paleontology; (2) structure and metamorphism; (3) Quaternary landscape evolution; and (4) engineering and environmental geology.
Note: In addition to the cited references, this list contains other pertinent maps and reports about the geology in the field-trip area.