WSP02105

• File Number: 8200.765
• Description: White River General
• State: CO
• Basin: Yampa/White
• Water Division: 6
• Date: 5/1/1986
• Author: Morrison-Knudsen
• Title: White River Geotechnical Study - Final Report - Volume I
• Water Supply Pro - Doc Type: Report/Study

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Frontier-Mowry Formations (Kfm) and Mancos Shale (Km)
To the northwest, at the 1 imit of the eastern map area, the Dakota Sandstone
di ps below a sequence of Cretaceous gray shales and interbedded sandstones.
The oldest unit is the Mowry Shale, which is characterized topographically by
a trough between the Dakota Sandstone and the overlying Frontier Sandstone.
The sandstones form resistant hogback ridges striking northeast. The Frontier
Sandstone, in turn, dips below the gray Mancos Shale to the northwest to form
the broad rolling topography bordering Agency Park just upstream of Meeker.

Iles (Ki) and Williams Fork (Kw) Formations
The western map area is bordered on 'the east by the Grand Hogback, a
monoclinal ridge of resistant Cretaceous rocks dipping steeply to the west.
The monocline is formed by the Iles and Williams Fork Formations which overlie
the Mancos Shal e and are predomi nantly 1 i ght colored massi ve sandstones wi th
thin shale interbeds and coal seams.

Wasatch Formation (Tw)
The broad flat valley known as Powell Park west of the Grand Hogback is
fl anked and underl ai n by the Terti ary Wasatch Formati on. It is composed of
variegated fine sandstones, siltstones, and claystones more than 5000 feet in
thickness. Weatheri ng of these weak rocks has produced a gently roll ing
topography with low buttes formed by the more resistant sandstone layers.

Lower Member Green River Formation (Tgl)
At the west end of Powell Park the White River enters into a broad valley
incised into the youngest rocks in the lower western end of the study area.
The oldest of these is the Tertiary Lower Member of the Green River Formation
which conformably overlies the Wasatch Formation. It is about 2,000 feet
thi ck and is composed of interbedded sandstones and shal es. The sandstone
ranges from fine-grained, well-rounded, well-sorted, thinly-bedded quartz
sandstone to coarse-grained; moderately-sorted, crudely cross-bedded
feldspathic sandstone. The sandstone units range in thickness from a few feet
to over one hundred feet. While some thick sandstone units are continuous
throughout the project area, many uni ts are 1 ense-shaped and di sconti nuous

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