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' CHAPTERTHREE Affected Environment ' Douglas Creek Member is approximately 800 feet thick, and the Garden Gulch Member is about 700 feet thick (Bradley 1931). The Anvil Points Member is similaz in composition and is actually a lateral correlative of the Douglas Creek and Gazden Gulch Members, as well as being part of the lower Pazachute Creek Member. Wasatch and Lower Tertiary Formations ' The Wasatch Formation may reach a maximum thickness of 5,500 feet, making this stratigraphic sequence the thickest Tertiary unit in the Piceance Creek Basin. In the southern and eastern ' portion of the basin, the Wasatch Formation has been subdivided into the Shire, Molina, and Atwell Gulch Members. The Shire Member has variegated siltstone, claystone, and sandstones. The Molina Member is dominated by massive, cross-stratified sandstone. The basal Atwell Gulch Member is composed of vaziegated siltstone and claystone (Donnell 1961). The Wasatch Formation is undivided in the northern part of the basin. The base of the Tertiary section is composed of a conglomerate formerly called the Ohio Creek Formation, which overlies Cretaceous rocks of the Mesa Verde Group (Hunter Canyon or Williams Fork Formation). 3.1.2 Project Area Geology 3.1.2.1 Piceance Site The predominant surficial geologic formation that outcrops at the Piceance Site is the Uinta Formation (Figure 3.1-3). There aze two units of the Uinta Formation, Unit 4 (TU,) and Unit 5 (TUS), that outcrop in Sections 17 through 21, 28, and 29. Unit 4 occurs from the Piceance Creek valley floor at elevation 6,100 feet msl up to 6,300 feet msl along Horse Draw and up to 6,420 feet msl in the center of Section 20. Unit 4 is a buff to brown, cliff-forming sandstone with a maximum thickness of 350 feet. Towazd the southwest, this unit thins and contains ' increasing proportions of silty mazlstone and siltstone. Unit 5 occurs in the western part of the Piceance Site. Unit 5 starts at about 6,380 feet msl along Horse Draw and at about 6,460 feet msl in the center of Section 20 and extends up to 6,650 feet ' msl. Unit 5 is a brown to buff, weathered sandstone with minor concentrations of siltstone in its eastern portion. The sandstone has been described as channel-formed, cross-stratified, medium- to fine-grained. The sequence contains increasing proportions of gray and greenish-gray siltstone ' interbedded with ledge-forming sandstone towazd the west. Thickness varies between 280 and 500 feet. ' Between Unit 4 and Unit 5 is a 40- to 60-foot-thick sequence of the Thirteenmile Creek Tongue (Tgtu) of the Eocene Green River Formation. The upper part of the Thirteenmile Creek Tongue is composed of a light gray to white weathered mazlstone. South of the Piceance Site, the Thirteenmile Creek Tongue contains three to four thin, rich oil shale beds. North of the Piceance Site, the mazlstone contains a few thin, porous ostracod chazophyte-bearing limestone beds. In addition to the Uinta and Green River Formations, Quaternary Holocene alluvium is found in the dry washes and the Piceance Creek valley floor. The alluvium consists of silt, sand, and Geology 3-5