Abstract The central Niobrara River valley in northern Nebraska(Fig. 1) has played an important role in the conceptual development of late Tertiary stratigraphy and vertebrate paleontology in the Great Plains. Much of our current understanding of the evolution of such mammals as horses, camels, and proboscideans is based on fossils collected from the Valentine and Ash Hollow Formations exposed in the deep (by Nebraska standards!)canyons of the Niobrara River and its tributaries in Brown, Cherry, and Keya Paha Counties. The Valentine-Ash Hollow sequence in this area represents the northernmost expression of a complex of alluvial deposits collectively known as the Ogallala (variously termed agroup or formation) which blankets much of the Great New Mexico. The only paved road to traverse reasonably good exposures of the classic Ogallala sequence in the Niobrara valley is Nebraska 12 about 3 mi (4.8 km) northeast of Valentine. Two adjacent road cuts at the northwestern margin of Fort Niobrara National Wildlife Refuge (see. 22, T.34N., R.27W., Cornell Dam Quadrangle, Fig. 2) expose nearly the entire thickness of the Valentine Formation and the Cap Rock Member of the Ash Hollow Formation. Examination of the road cuts, combined with a tour of the Refuge, will provide the visiting geologist with an overview of the later Tertiary mantle of the Great Plains near the boundary between the latter physiographic province and the Central Lowlands Province to the east. Geomorphological relation ships are also exceptionally clear along this segment of the Niobrara River; the very late

Abstract The outcrops of the Dakota Group and the Graneros Shalenental sandstones. As the viewer examines younger rocks toward Greenhorn Limestone interval of LateCretaceus age at Ponca the northwest, the original environments of deposition change, State Park provide an excellent sedimentary record of the last and these deposits give way to lagoonal, estuarine, or tidal and great marine invasion of the North American midcontinent. The mudflat deposits, which are finally overwhelmed by marine southeastern end of the outcrop area consists of the older continental sandstones. As the viewer examines younger rocks toward. the northwest, the original environments of deposition change, and these deposits give way to lagoonal, estuarine, or tidal and mudflat deposits, which are finally overwhelmed by marine shales and limestones.

Abstract Scotts Bluff National Monument is best reached by starting from the junction of Nebraska 71 and 92 in downtown Gering, Nebraska, and proceeding westward on Nebraska 92 for 2.4 mi(3.4 km) to the visitor center (Fig.1). The monument is open from 8 A.M. to 8 p. M. Memorial Day to Labor Day, 8 A.M. to 6 p. M. Labor Day to October 1, and 8 A.M. to 5 p. M. October 1 to Memorial Day. Educational groups are not charged the nominal usage fee for admittance to the summit road and parking(Fig.2). Please stay on the trails and note that collecting rocks or other items is prohibited without a permit from the National Park service.

Abstract From a high point on the south side of the Platte Valley, 4.7 mi (7.5 km) west of Fremont (Fig. 1) and 1.8 mi (2.9 km) north of Cedar Bluffs (SE½SE½ Sec.22, T.17N., R.7E.; Fremont West 7¼-minute Quadrangle), one can view the present Platte River and valley as well as look across an abandoned valle segment through which at least part of the Platte River once flowed (Fig. 2). In addition, the south bluffs of the Platte, which have remained cleanly swept exposures of a large partof the Pleistocene record of eastern Nebraska since before 1900, can be seen from across the river in Hormel Park (N edge SW½Sec.34, T.17N., R.8E.) (Fig.3). To reach the overview point, follow Nebraska 109 north from Wahoo to Cedar Bluffs, go east 0.25 mi (400 m), then north 2 mi (3.2 km) to County Road 2. Turn west 0.1mi (0.2 km) and stop at the top of the slope (Fig. 1). To reach Hormel Park in Fremont, return to Nebraska 109 and turn east 5 mi (8 km). At U.S. 77, turn northfor 1.5 mi (2.5 km), then west 0.4 mi (0.6km). Follow the gravel road to the southwest about 0.2 mi (0.3 km)to Hormel Park. Drive about 0.2 mi (0.3 km) farther, park, and walk to the edge of the Platte River. Field glasses are useful to examine the bluffs, which are across the river, about 600 ft(200 m) away. Both the overview point

Abstract The Duer Ranch locality is situated on either side of U.S. 26 in southeastern Merrill County, Nebraska, halfway between the villages of Lisco and Broadwater and about 54 mi (90 km)southeast of Scottsbluff, Nebraska. The Rush Creek Land and Livestock Company currentlyowns all of sections 28, 29, 33, 34, and 35 of T. 19 N., R.47 W., as well as parts of sections 2, 3, 4, 10, and 11 of T. 18N., R.47W. (Broadwater and Tar Valley SW, 7½-minute Quadrangles; Fig. 1). The owners have allowed geologists to study the exposures on ranch property providedthat visitors stop at the ranch headquarters (Fig. 1) and obtain permission from the ranch foreman. Vehicles shouldbe parked inside the gate on thenorth side of U.S. 26 in the SW¼ Sec. 3, T.18N., R47.W. (Fig. 1), and all study ofthe site should be done on foot.Be certain to closeany gates that you open, anddo not smoke on the property. Rattlesnakes are found on the ranch. If you have asmall group and wish to examine the exposures in the southeast corner of the locality, two vehicles can park safely along the north side of the road cut on U.S. 26 in the NE¼ NW¼ sec. 10, T.18N., R.47W.

Abstract Ash Hollow State Historical Park, administered by the Nebraska Game and Parks Commission, is located primarily in Sec. 3, N½, Sec. 10, and the E½NE¼Sec.22, T.15N., R.42W. (Fig. 1), Garden County, Nebraska. The park and adjacent lands are shown on the Lewellen and Ruthton 7½ -minute Quadrangles; scale 1:24,000. U.S. 26 passes through the park. This highway and other paved roads provide access from 1-80. A camping area and a museum with excellent interpretive displays are located in the park. Rock exposures are easily accessible by foot in the park and at road cuts along U.S. 26 and nearby county roads. No collecting of specimens is permitted in the park, but samples may be collected from road cuts. Fossils found by people in and near the park have been added to the museum collections. Poison ivy can be found in abundance in some parts of the area. Rattlesnakes may live anywhere in this part of Nebraska.

Abstract This outcrop of Pennsylvanian and Permian rocks is along the east side of Nebraska 105 about 3 mi (5 km)south of Humboldt in Richardson County, Nebraska. It is located in the SW¼ Sec. 22 and NW¼ Sec. 27, T.2N., R.13E., as shown in Fig. 1, which reproduces a small part of the Humboldt SW 7½-minute Quadrangle. The rocks are exposed on public right-of-way in the road ditch eastof the highway and are easily accessible by foot. Here is a good exposure of the contact between the Pennsylvanian and Permian rocks and also one of the best localities in Nebraska to observe steeply dippingrocks associated with the Humboldt Fault Zone. The exposure here is approximately 170 ft (51.8 m) thick. The dip is 17°E.

Abstract Excellent outcrops of Niobrara and Pleistocene strata can be seen near Franklin and Bloomington (Exposures 1 and 2, Fig. 1; Figs. 2-5) in Franklin County. The Niobrara Formation generally dips westward at about 15 ft/mi (3 m/km), and at the western end of the outcrop area in Harlan County, the Niobrara is conformably overlain by the Pierre Shale. All of the outcrops are road cuts and are within public access. The outcrop near Franklin has a very steepnorth slope and a fairly gentle east slope. The section at the Bloomington bridge is very steep but negotiable by persons without physical limitations. The outcrops near Red Cloud are fairly steep but are also negotiable by persons without physical limitations.

Abstract Extensive sections along the Nelson River in northern Manitoba lie within NTS sheet 54 D (1:250,000). The nearest town, Gillam, can be reached by air or road from Winnipeg, Manitoba.From Gillam, follow the road eastward across Long Spruce Dam and proceed toward Sundance. Access to each site (Fig. 1) is obtained by parking the vehicle along the roadside and walking a very short distance to the bluff.

Abstract The Seagull Lake-Gunflint Lake area along the Gunflint Trail (Cook County Highway 1) in T. 65N., R. 3 and R. 4W. in the northwestern part of Cook County, Minnesota (Fig. 1) is north of Grand Marais, the county seat and starting point for the Gunflint Trail. Although accessible by automobile or bus, much of the site is rugged and heavily wooded and requires considerable off-road travel. Except for obvious resorts and summer homes, the site is on public lands managed by the U.S. Forest Service. There is no single place where the entire geologic succession is laid out for easy study, so one must visit several localities to appreciate the significance of the area. This guide suggests 12 stops (Figure 2) that can be easily visited in one day and that collectively illustrate the major rock types and their stratigraphic and structural attributes. However, exposureis of such quantity and quality that independent exploration is heartily encouraged.

Abstract The western Vermilion district is located in northeastern Minnesota, about 18 mi (30 km) north of the towns of Virginia and Aurora on the Mesabi iron range (Fig.1). The major towns in the western Vermilion district are Cook, Tower, Soudan, and Ely. The area to be described here lies within the Tower and Soudan 7¼-minute Quadrangles (Fig. 1).

Abstract Three specific outcrop areas are included: (1) Lakewood, 2.1mi (3.5 km) northeast of the Lester River (in Duluth, Minnesota)on St, Louis County 61 (S¼ Sec. 34, T.5lN., R.13 W.; Lakewood7¼-minute Quadrangle), in Congdon (city) Park; (2) Two Harbors,0.5 mi (0.8 km) south of U.S. 61 on First Street(NW½ Sec. 6, T. 52N., R. 10W.; Two Harbors 7¼-minute Quadrangle), in Burlington Bay(city) Tourist Park, and (3) GooseberryFalls, 13.5 mi (23 km) northeast of Two Harbors on U.S. 61(SW½ Sec. 22, T. 54N., R. 9W., Split Rock Point 7½-minute Quadrangle), in Gooseberry Falls State Park. Note: State Park rules prohibit defacing or collecting rocks. Removal of bedrock specimens showing the special structures in all areas is strongly discouraged for the benefit of future observers.

Abstract The Duluth Complex underlies an area of approximately 2,265 mi 2 (6500 km 2 ), but over much of its extent it is covered by glacial deposits. Some of the best and most representative exposures are in the city of Duluth. Several outcrops are described here along the Skyline Parkway, a well-marked scenic road near the top of the slope on which Duluth is built, facing the Lake Superior Basin. They are in the West Duluth, Duluth Heights, and Duluth 7½-minute Quadrangles. The first stop is adjacent to I-35 just southwest of Duluth (Fig. 1).

Abstract Jay Cooke State Park occupies nearly 15 mi 2 (38 km 2 ) in the northeastern corner of Carlton County in T.48N., R.15 and 16W. (Fig. 1). It is about midway between the village of Thomson and Fond du Lac, the westernmost suburb of Duluth. The park may be reached by following Minnesota 210 from the Carlton-Cromwell interchange with I-35 eastward for approximately 3.5 mi (6 km) through the town of Carlton to the St. Louis River. Immediately after crossing the river at Thomson, the highway turns sharply to the south and 0.1 mi (0.2 km) later enters Jay Cooke State Park (Fig. 2). The Park Headquarters, a picnic area, and an information building are located approximately 2 mi (3.4 km) intothe park. As with all Minnesota state parks, a daily fee or a yearly permit is required to use the park facilities. Minnesota 210 continues through the park along the north side of the St. Louis River for an additional 5.5 mi (9.3 km) where it joins Minnesota 23 in Fond du Lat.

Abstract Pipestone National Monument is located in parts of sections 1 and 2, T.106N., R.46W., north of the City of Pipestone, Pipestone County, southwestern Minnesota (Fig. 1). The monument is located 0.9 mi (1.5 km) northwest of the intersection of U.S. 75 and Minnesota 23. Proceed north on U.S. 75 for 0.4 mi (0.7 km); turn west and follow monument signs 0.5 mi (0.8 km) to the entrance. As with all national parks and monuments, no samples may be collected without a permit from the Department of Interior, U.S. National Park Service.

Abstract Gitchie Manitou State Preserve is located in the northwesternmost corner of Iowa, in the W½, Sec. 11, T. 100N., R. 49W., about 9 mi (14,5 km) northwest of Larchwood in Lyon County, Iowa (Fig. 1). The preserve is situated in the valley of the Big Sioux River, which forms the western limits of the preserve and the boundary between Iowa and South Dakota. The highest elevation within the preserve is about 1,286 ft (392 rlevel, about 40 ft (12 m) above river level but about below the elevation of nearby upland areas.

Abstract The oldest Paleozoic rocks exposed in Iowa are found in the northeastern corner of the state in Allamakee County. Cambrian exposures in the county form part of the classic reference area in the Upper Mississippi Valley for the Upper Cambrian Croixan Series. Overlying dolomites of the Prairie du Chien Group are exposed as bold cliffs in the bluffs along the Mississippi River and its tributaries. Cambrian and Lower Ordovician strata collectively encompass the Sauk Sequence, the first large-scale transgressive-regressive cratonic marine cycle of the Phanerozoic (Sloss, 1963). A major episode of erosion followed deposition of the Sauk Sequence. A widespread unconformity separates Lower and Middle Ordovician strata in the region, marking the boundary between the Sauk Sequence and the succeeding Tippecanoe Sequence. The most complete sequence of Cambrian and Ordovician strata in northeast Iowa is exposed between Lansing and Church as one ascends from the Mississippi River up the valley of Clear Creek to the crest of Lansing Ridge along Iowa 9 (Fig. 1) 1). Vertical relief along this profile is 630 ft (192 m), and the composite stratigraphic section measured totals 619 ft (189 m). The base of the section begins along Iowa 26 north of the Mississippi River bridge (loc. 1, Fig. 1), and continues through a series of roadcuts and natural exposures in Mount Hosmer Park (loc. 4, Fig. 1). Strata equivalent to the lower half of the section at locality 1 can be seen behind Knopf’s Standard Station

Abstract There are three principal exposures of the Lime Creek Formation in the area between Mason City and Charles City, northern Iowa. By a considerable margin, the most extensive site is the quarry of the former Rockford Brick and Tile Company, only 1 mi (1.6 km) west of town in Floyd County (NW¼Sec. 16, T.95N., R.18W.). The Juniper Hill State Preserve is 0.5 mi(0.8 km) to the northwest. Bird Hill is located just a fe miles farther west at a road cut on an east-west county right-of-way in eastern Cerro Gordo County (NE½Sec.24, T.95N., R.19W.). The stratigraphic section known historically as Hackberry Grove, now called Claybanks Forest, lies just south of the Winnebago River (near center NE½Sec.34, T.96N., R.19W.). The Winnebago River was originally called Lime Creek (hence the name Lime Creek Formation). A location map (Fig. 1) has been prepared from the general highway and transportation maps of Cerro Gordo and Floyd counties. Topographic sheets for the Mason City Southeast and Rockford 7½-minute Quadrangles cover the area. The Rockford Brick and Tile property lies adjacent to County Road B47, west of Rockford. The kilns have been inactive for several years, and permission to visit the grounds must be secured from the present owner, Allied Construction Company, 1211 South Main Street, Charles City, Iowa 50616. Bird Hill is also situated on County Road B47, with a large parking area on the north side of the road. The site has recently been designateda State Preserve. At Hackberry Grove, the Claybanks

Abstract Gutenberg is a picturesque community nestled in the Mississippi River Valley, where local relief approaches 400 ft (120 m). Lock and Dam No. 10 at Gutenbergis a major conduit for upper Mississippi barge traffic. Visitors can view the lock in operation at close range from an observation platform. Excellent roadcuts and many additional exposures of Middle Ordovician strata are easily accessible in the Gutenberg area, where virtually every bed is available in continuous fresh exposures over a stratigraphic interval of more than 250 ft (75 m).Three reference sections (Fig. 1B) enable the sequence of Ordovician formations (St. Peter, Glenwood, Platteville, Decorah, Dunleith, Wise Lake) to be composite for general discussion (Fig. 2) :1) Gutenberg South Roadcut, US. 52 (SW¼Sec.29, T.92N., R.2W.), a superb continuous section that offers a spectacular view of the Mississippi River (Delgado, 1983); 2) Gutenberg North Roadcut, U.S. 52 (SW¼SW¼Sec.5 and NW¼Sec.8, T.92N., R.2W.), a well-studied but now partly overgrown sequence (Templeton and Willman, 1963; Bakush, 1985); and 3) X56 Roadcut, Great River Road (NW¼NW¼Sec.32 and SW¼SW¼Sec.29, T.93N., R2W.), a similar sequence to Gutenberg North, but better exposed by recent road construction. Excellent exposures of Lower and Middle Ordovician rocks are also accessible at Clayton (especially private barge terminal road) and the Pikes Peak State Park area (Fig. 1A). Good exposures of Jordan Sandstone (Cambrian) can be seen along the river from McGregor north to Effigy Mounds (Fig. 1A). Ordovician stratigraphic terminology in

Abstract Cretaceus exposures in the Sioux City area, primarily along the Big Sioux River in Iowa and the Missouri River Valley in northeast Nebraska, were of considerable importance in the early formulation of stratigraphic nomenclature in the Western Interior Province (Tester, 1931). It was from this area that Meek and Hayden (1862) originally named the “Dakota Group,” the basal subdivision of Cretaceus rocks as used throughout much of the western U.S. A summary of Cretaceus stratigraphy and paleogeography in the Iowa area is given by Witzke and others (1983). The east side of the Big Sioux River Valley reveals a series of Cretaceus exposures (Fig. 1) that are among the best in Iowa. Many of the exposures are along the Iowa 12 right-of-way and are publicly accessible (localities 1, 2, 3, 4, 8). Roadside exposures in Stone State Park (localities 5, 6) and old shale pit operations at Kirk Hanson Recreation Complex in Riverside (locality 9) are also publicly accessible, but collecting is discouraged. Other exposures are on private land, and permission must be secured before entering (e.g., shale pit of Siouxland Sand and Gravel, locality 7). Many of the exposures are extremely steep and potentially hazardous; please exercise caution. A general description of Cretaceus rock units examined and measured at localities 1 through 9 (Fig. 2) is given in the Measured Section. Strata at locality 10 (Fig. 2) are poorly exposed and the illustrated section is adapted from