Field Trip Road Log From Casper to Midwest, Wyoming: 41 MILES (Summarized from road logs by Curry and Crews (1976) and Whitehead (1986); revisions and additions by R.M. Flores).  Figure 1 shows the route of the field trip.

Leave Parkway Plaza Parking lot-TURN LEFT and then LEFT onto Interstate 25 on-ramp. Proceed north on Interstate 25 toward Midwest.  Casper Mountain (elevation approximately 8,100 feet) dominates the skyline to the south, which is the northern extent of the Laramie Mountains.  These mountains bound the southern limit of the Powder River Basin (Fig. 2).

The North Platte River (mile marker 188.2) is one of the major rivers of the Powder River Basin, yet its drainage basin includes only a small fraction of the present structural basin.  The North Platte River originates in the North Park Basin of north central Colorado and flows northward across southern Wyoming, cutting through present topographic features (characteristic of superposed drainage).  The river slices through the western end of Casper Mountain at Bessemer Narrows and then flows eastward across the southernmost Powder River Basin to exit over the Hartville Uplift to the southeast.

Casper is at the northeastern limit of the "Wyoming Wind Corridor," a major wind-channel crossing southern Wyoming.  A broad topographic low in the Continental Divide in the area of the Great Divide (Red Desert) Basin forms a natural channel for the regional flow of westerly winds from the Great Basin. The Casper dune field (north of the city of Casper) was formed in response to west-to-east winds blowing northeastward from the "Wyoming Wind Corridor" through gaps in the Crooks-Green-Ferris-Seminoe Mountain trend. The dune field, with the exception of a few blowouts is now mostly stabilized.

Well-developed, large pebble-and cobble-sized ventifacts (wind-polished stone) are found on deflation surfaces formed on the terrace gravels of the North Platte River.  Individual clasts are polished and faceted by wind-driven dust and sand, producing dreikanter (doubly pointed) shapes. Deeply pitted and fluted surfaces on ventifacts are rare here. The best-developed ventifacts seem to be cut on dense, hard rock, especially quartzites. Coarse-grained plutonic rocks show little, if any, ventifact development. Ventifacts developed on carbonates and sandstones are rare on the intensely weathered upper surface of the terrace gravel.

North of the Interstate 25 Bypass (mile marker 188.5), we descend a hill and leave the Casper dune field (mile marker 190.3) into the Cody Shale (Upper Cretaceous).  For the next 15 miles, we will be slowly moving up-section within the Upper Cretaceous series (Fig. 3). At 2 o'clock (northeast) is a view of Soda Lake. This lake, in a natural depression, is a wastewater disposal pond for the freshwater effluent of the Amoco Refinery.  The water supports a diverse migratory bird population and is regularly visited by the local Audubon Chapter.

Cross the underpass for Wardwell Road, Exit 191 (mile marker 191).  The cluster of houses coming up on the left (west), marked by a red-capped, blue water tower, is the town of Bar Nunn.  Bar Nunn is built around the old Wardwell Airport (old Casper Airport) of World War II vintage.  Shortly (at 10 o'clock), you will be able to look down the old (east-west) runway, now with houses on either side and converted into a wide street.  This town certainly has the bragging rights for the widest streets in the West.  On the right is a grassy roadbed that intersects the interstate.   This road is the "old road" (pre-U.S. 25/87) from Casper to the Salt Creek oil and gas field. The right lane (northbound) is concrete and the left lane is asphalt aggregate.

Cross another underpass (mile marker 194.34) while ascending a gentle slope.  A borrow pit is on the left (west) at the crest of a low hill. This low, east-west-trending hill of alluvial sand and gravel is mapped as Quaternary terrace or gravel, pediment, and fan deposits.  This deposit presumably represents a high-level channel remnant of a west-to-east flowing stream, ancestral to the present-day Casper Creek.  Casper Creek originates in the Rattlesnake Mountains, flows across the Wind River Basin and crosses the Casper Arch (west of our location) to join the North Platte River at Casper.

The sandstone bluffs (mile marker 196) on the left (west) are outcrops of the Teapot Sandstone Member of the Mesaverde Formation (Upper Cretaceous). The outcrops are named The Reefs.   A "reef' in a geomorphic sense is an old-time term used, especially in the western United States, for a jagged outcrop or hogback that was a barrier to travel. The highway is on the Lewis Shale (Upper Cretaceous; see Fig. 3), which is largely covered by Quaternary sediments.

To the right (east) of the interstate (mile marker 196), about three-fourths of a mile, is a white-roofed building. This building is part of Nine Mile Lake, an acidic, in-situ, uranium-leaching plant of Rocky Mountain Energy.  The uranium (as Uraninite) is in a roll-front type deposit (ore body) at a depth of 500 to 550 feet, in the Teapot Sandstone (see Fig. 3).  Sulfuric acid and hydrogen peroxide were injected in a five spot pilot-test area from 1977 to 1978.  The Wyoming Department of Environmental Quality requires in situ operators to restore groundwater quality to baseline conditions.  From 1978 to 1979, a restoration project, consisting of injection of a mixture of native groundwater and treated, produced water, restored groundwater quality in the leached zone.

Cross the underpass for Ormsby Road - Exit 197 (mile marker 197).  At 3 o'clock (about 2 miles east of the interstate) are tank batteries for the Midway oil field.  The field, discovered in 1931, is producing oil from a structural trap in the Frontier Formation (see Fig. 3).  Cumulative production (as of February 1990) is 373,801 barrels of oil (BO), no gas, and 30,706 barrels of water (BW).  The low hills to the right (east), forming the skyline, are developed in the Fox Hills Sandstone (Upper Cretaceous; see Fig. 3).  Their rounded, streamlined appearance suggests that they may be yardangs (sharp-crested ridges between round-bottom troughs carved out by wind).

Re-enter the Casper dune field, which occurs, on a narrow, west-to-east trend, extending from the interior of the Wind River Basin across the Casper Arch to the edge of the Powder River Basin.  Based on the map patterns of preserved rocks, this area is also an east-west-trending structural low for the Casper Arch.  Quaternary sands occupy this structural low of probable Laramide age.

On the right (east) at 3 o'clock, near the skyline, is a glimpse of an active dune blowout.
Cross McPherson Draw (mile marker 202.5) and leave the dunal topography.  The hill at 1 o'clock is capped by the Lance Formation (Upper Cretaceous; see Fig. 3). Begin a slow drift downsection (see Fig. 3) for approximately 20 miles.  On the right (east) is the community of Antelope Hills (mile marker 205-206), built on the Lewis and Fox Hills Formations (Upper Cretaceous; see Fig. 3). 

At mile marker 207 is the Twenty-Mile Hill.  At 11 o'clock is a microwave relay station. To the right (northeast), there is a brief glimpse of Pine Ridge, developed on Fort Union (Paleocene) rocks.

At mile marker 210 is the TURNOFF to Highway 259 toward Midwest.  The outcrops (mile marker 11.7) on the right (east) include the Upper Cretaceous Lewis Shale (Mowry Shale) overlain by the Fox Hills Sandstone (see Fig. 3).  The coal-bearing Teapot Sandstone exposed on the left or west (mile marker 12) underlies these rocks.  The “Teapot rock” is exposed immediately north of the Teapot Ranch at mile marker 14.82.  This is the type locality of the Teapot Sandstone (Curry, 1976b).  Marine shale (mile marker 16) and the coal-bearing Parkman Sandstone (from mile marker 16 to 17.6) underlie the Teapot Sandstone (see Fig. 3).  The Parkman Sandstone is underlain by the Cody Shale (see Fig. 3) exposed in the central part of the Teapot Dome (mile marker 21).  The road to the U.S. Naval Petroleum Reserve No. 3 toward the Teapot Dome field is at mile marker 21.7.  Read “Tempest in the Teapot” for summary of the Teapot Dome field controversy.   North of the Teapot Dome field is the Salt Creek Anticline field (mile marker 24-25).  The field is flanked on the east (right) and west (left) by the Upper Cretaceous Shannon Sandstone from mile marker 23.5 to Midwest (read summary of Salt Creek field on page 9). 

Alternate route: 

Continue on Interstate 25 from the Highway 259 TURNOFF.  The next 24 miles goes gradually downsection through the Mesaverde Formation, Cody Shale and Frontier Formation (Upper Cretaceous; see Fig. 3).  The Mesaverde Formation contains bituminous coal beds interbedded with fluvial-deltaic channel sandstones and floodplain siltstones and shales.  The Cody Shale includes the Carlile, Niobrara, and Steele Shales in the lower part and the Sussex and Shannon Sandstones in the upper part.  The Frontier Formation is exposed along the flanks of the Tisdale Mountain Anticline (Merewether and others, 1976).