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Outcrops of the lower and upper units were sparse in the <br />mapped area since much of the formation is covered by vegetation • <br />and a variable thickness of soil and humus. Wherever field <br />measured dips are mapped within the area underlain by Williams Fork <br />there is an outcrop. <br />3.1.3 Itewis Shale. Bass, et. al. (1955, p. 159) indicate "The <br />Lewis shale consists chiefly of dark-gray to bluish, homogenous <br />marine shale." In the project area the Lewis crops out on both the <br />eastern and western flanks of the Fish Creek anticline. The Lewis <br />underlies all but the northeastern part of the area generally west <br />of Routt County Road 27. <br />The Lewis weathers generally to a uniform light tan, and only <br />limited exposures of bedrock were found in the area mapped. • <br />Several exposures of Lewis were mapped along the major northernmost <br />drainages that pass through secs. 28 and 29. The best exposure is <br />about 1600 feet east of the center of sec. 29. Here the formation <br />is primarily shale, dark brown to black, gypsiferous and with tan <br />or orange sandstone nodules. Other limited exposures of Lewis <br />occur in the drainages about 600 feet to the northwest and about <br />2800 feet to the southwest. The lower part of the Lewis, <br />immediately above its contact with the Williams Fork Formation, <br />contains sandy beds that are moderately resistant to erosion. <br />The Lewis apparently weathers deeply in most places, and the <br />depth to which it is weathered is variable throughout the area. <br />About 1600 feet northeast of the center of sec. 5, open, deep soil <br />fractures were mapped along a relatively steep topographic slope. • <br />Only the upper four to six feet of weathered shale could be <br />12 <br />