ABSTRACT Seattle’s geologic record begins with Eocene deposition of fluvial arkosic sandstone and associated volcanic rocks of the Puget Group, perhaps during a time of regional strike-slip faulting, followed by late Eocene and Oligocene marine deposition of the Blakeley Formation in the Cascadia forearc. Older Quaternary deposits are locally exposed. Most of the city is underlain by up to 100 m of glacial drift deposited during the Vashon stade of Fraser glaciation, 18–15 cal k.y. B.P. Vashon Drift includes lacustrine clay and silt of the Lawton Clay, lacustrine and fluvial sand of the Esperance Sand, and concrete-like Vashon till. Mappable till is absent over much of the area of the Vashon Drift. Peak local ice thickness was 900 m. Isostatic response to this brief ice loading was significant. Upon deglaciation, global ice-equivalent sea level was about −100 m and local RSL (relative sea level) was 15–20 m, suggesting a total isostatic depression of ~115–120 m at Seattle. Subsequent rapid rebound outstripped global sea-level rise to result in a newly recognized marine low-stand shoreline at −50 m. The Seattle fault is a north-verging thrust or reverse fault with ~7.5 km of throw. Conglomeratic Miocene strata may record initiation of shortening. Field relations indicate that fault geometry has evolved through three phases. At present, the north-verging master fault is blind, whereas several surface-rupturing faults above the master fault are south verging. The 900–930 A.D. Restoration Point earthquake raised a 5 km × 35 km (or larger) area as much as 7 m. The marine low-stand shoreline is offset by a similar amount, thus there has been only one such earthquake in the last ~11 k.y. Geomorphology is largely glacial: an outwash plain decorated with ice-molded flutes and large, anastomosing tunnel valleys carved by water flowing beneath the ice sheet. Euro-Americans initially settled here because of landscape features formed by uplift in the Restoration Point earthquake. But steep slopes and tide flats were not conducive to commerce: starting in the 1890s and ending in the 1920s, extensive regrading removed hills, decreased slopes, and filled low areas. In steep slopes the glacial stratigraphy is prone to landslides when saturated by unusually wet winters. Seismic hazards comprise moderately large (M 7) earthquakes in the Benioff zone 50 km and more beneath the city, demi-millennial M 9 events on the subduction zone to the west, and infrequent local crustal earthquakes (M 7) that are likely to be devastating because of their proximity. Seismic shaking and consequent liquefaction are of particular concern in Pioneer Square, SoDo, and lower Duwamish neighborhoods, which are largely built on unengineered fill that was placed over estuarine mud. Debris from past Mount Rainier lahars has reached the lower Duwamish valley and a future large lahar could pose a sedimentation hazard.

ABSTRACT With a thick and highly variable mixture of glacial and nonglacial soils overlying bedrock, punctuated by seismically active fault zones, Seattle is a challenging arena for geologists, engineering geologists, and geotechnical engineers. Because of this geologically complex stratigraphy, Seattle has a higher density of geoprofessionals and subsurface explorations than other cities of equal size. Even so, the subsurface always delivers surprises when construction begins. By visiting three major civil works, SR 520 floating bridge, Alaskan Way Viaduct/SR 99 tunnel, and the Beacon Hill Transit tunnel, you will discover the interaction between Seattle geology and the engineering that made these projects successful.

Abstract The siege of Petersburg and Richmond during the American Civil War in 1864–1865 provides a stellar example of how geology can affect military operations and thus the course of history. During the Union drive to take the Confederate capital, they used Virginia’s broad tidal rivers on the Atlantic Coastal Plain as supply lines for their huge army. During the siege, both sides took advantage of the unconsolidated Cenozoic sediments of the Coastal Plain to create a new style of combat—trench warfare—which would be taken to horrifying extremes in World War I. This trip visits seven sites of both historic and geological significance in the Petersburg area.

Abstract With its wide variety of geological features and phenomena packed into a small area, the Baraboo of south-central Wisconsin is among the most visited parts of the Midwest by geology students. This guidebook, the first comprehensive look at the area in decades, covers the spectrum of geological features present in the area, and it is useful as a teaching tool. An exceptional outdoor classroom, the Baraboo area contains a spectrum of geology, including excellent examples of geomorphology, glacial geology, structural geology, petrology, stratigraphy, and sedimentology. Ages of the strata range from 1.7-billion-year-old Precambrian to the Quaternary. The area has been studied for about a century, but it still holds surprises for professionals and students alike.

Abstract This two-day field trip focuses on the geology and geomorphology of the Carolina Sandhills in Chesterfield County, South Carolina. This area is located in the updip portion of the U.S. Atlantic Coastal Plain province, supports an ecosystem of longleaf pine ( Pinus palustris ) and wiregrass ( Aristida stricta ), and contains three major geologic map units: (1) An ~60–120-m-thick unit of weakly consolidated sand, sandstone, mud, and gravel is mapped as the Upper Cretaceous Middendorf Formation and is interpreted as a fluvial deposit. This unit is capped by an unconformity, and displays reticulate mottling, plinthite, and other paleosol features at the unconformity. The Middendorf Formation is the largest aquifer in South Carolina. (2) A 0.3–10-m-thick unit of unconsolidated sand is mapped as the Quaternary Pinehurst Formation and is interpreted as deposits of eolian sand sheets and dunes derived via remobilization of sand from the underlying Cretaceous strata. This unit displays argillic horizons and abundant evidence of bioturbation by vegetation. (3) A <3-m-thick unit of sand, pebbly sand, sandy mud, and mud is mapped as Quaternary terrace deposits adjacent to modern drainages. In addition to the geologic units listed above, a prominent geomorphologic feature in the study area is a north-trending escarpment (incised by headwater streams) that forms a markedly asymmetric drainage divide. This drainage divide, as well as the Quaternary terraces deposits, are interpreted as evidence of landscape disequilibrium (possibly geomorphic responses to Quaternary climate changes).

Abstract The surficial geology of the Baraboo area is very important because it includes the transition from a glaciated region to the Driftless Area. The eastern portion of this area was glaciated as part of the Green Bay lobe of the ice sheet in this area. The terminal moraine is present and is characterized by sandy till. No valid information that substantiates glacial activity exists west of the city of Baraboo. The Driftless Area includes a site of the earliest Wisconsin habitation.

Abstract This road log is different than most in a variety of ways. It is similar in that the stops are numbered in a certain order. That is because each stop must have some identification and numbers are the simplest and easiest to follow. Mileage is provided between stops, not in a cumulative fashion. This makes it easy to arrange the stops to suit the specific leader(s) and students. Those who use this field guide can choose to visit the stops in any order that they wish. The complete trip is designed to take two full field days, but stops can be visited in any fashion that suits the wishes and schedule of the group. There are a few alternate stops that may be used in addition to or in lieu of some of the regular stops. The estimated time necessary to spend at each stop is indicated in the log to help in organizing your trip. The total estimated time of the combined stops is ~12–14 hours. This does not include any travel time or lunch stops so that leaders can develop their own plans. Unless indicated in the figure caption, all figures herein are those of the co-authors. The trip starts at the intersection of Wisconsin Highway 33 with Interstates I-90 and I-94 (Appendix Figure A1.) Enjoy!

Abstract This guidebook volume is a compilation of field excursions offered at the 47th annual meeting of the North-Central Section of the Geological Society of America, held in Kalamazoo, Michigan, May 2013. These field trips examine a wide range of geological time intervals and topics, from Silurian salt, to Cretaceous cosmic impact, to newly interpreted Mississippian–Pennsylvanian Michigan stratigraphy, to Quaternary glacial landscape formation, sand dune development, and present-day coastal bluff stability/erosion issues. Trips geographically range throughout southern Michigan and northern Indiana from Detroit, Michigan, in the east to the Kentland Quarry in Indiana to the west. Early depositional events within the Michigan Basin are examined deep underground in the Detroit Salt Mine (trip leaders: W.B. Harrison III and E.Z. Manos [onsite leader]). This salt mine has been in operation for more than 100 years, and extends for miles beneath the city of Detroit. Kentland Quarry, located in northwest Indiana, is the site of a Cretaceous-aged meteorite impact (trip leader: J.C. Weber). This site allows for surface examination of a similar style impact event that occurred in now buried Ordovician-age (Trenton) rocks located in Cass County, (southwest) Michigan. Mississippian-aged fluvial deposits have been traditionally classified as the youngest bedrock exposed in Michigan. These rocks crop out in the center of the Michigan Basin near Grand Ledge, Michigan (trip leaders: N.B.H. Venable, D.A. Barnes, D.B. Westjohn, and P.J. Voice). Younger, more recently identified, Pennsylvanian rocks will be the subject of a related core workshop at the Michigan Geological Repository for Research and Education (MGRRE) in Kalamazoo (workshop leaders: S. Towne, W.B. Harrison, and D.B. Westjohn). The regional, surficial geology of southwest Michigan is highlighted by three field trips. The first trip details the glacial landforms and sedimentary features formed by the differing dynamics of the Michigan and Saginaw lobes of the Laurentide Ice Sheet (trip leaders: A.E. Kehew, A.L. Kozlowski, B.C. Bird, and J.M. Esch). The two other trips follow along the Lake Michigan eastern shoreline and examine development of sand dune complexes (trip leader: E. Hansen) and present-day, coastal bluff stability and erosion issues (trip leaders: R.B. Chase and J.P. Selegean).

A Google Earth–based virtual field trip, part of an introductory geology class, has been developed to illustrate the geology of the Presidential Range, New Hampshire. During a class field trip to Mt. Washington, the highest peak in the Northeast, students record GPS locations of exposures and collect information in the form of field notes and digital images from outcrops. Students upload the GPS waypoints into Google Earth and their images into a class PicasaWeb album, and they also make video clips that are uploaded into a class YouTube account. In Google Earth, the students embed and geologically annotate their images and embed their video clips. The final product is a Google Earth .kmz file or what is termed a mashup. The mashup provides a permanent record of the excursion and, if made available on the Internet, allows any user the ability to easily view the geology at any time. Constructing the mashup from the real field trip initiated reflective, independent, student-motivated learning and group work using technology that the students regularly use and enjoy doing. The resulting mashups have been very good, with an appropriate level of geologic content for an introductory course. Grading, which normally is onerous, is actually enjoyable, entertaining, and easy.