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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01'_:'3lt

They are Precambri an igneous and metamorphi c crystall i ne rocks composed of
granite, schist, quartzite, and gneiss. The crystalline rocks are overlain by
several hundred feet of lower Paleozoic sedimentary rocks of Cambri an and
Devonian age, including sandstone, dolomite, and limestone. The largest part
of the exposed uplift area, however, is formed by upper Paleozoic rocks of the
Pennsylvanian and Permian periods. These sedimentary deposits consist of dark
shale, yellow sandstone, gray limestone reefs, and evaporites overlain by more
than 3,000 feet of cl astic red beds rangi ng from shal e and mudstone to
sandstone and conglomerate; The Paleozoic rocks are in turn overlain by rocks
of the Mesozoi cEra consi sti ng of several thousand feet of red beds. The
younger rocks are alternating shal e, si 1 tstone, and sandstone of the Tri assic
Period and light-colored sandstones and dark marine shales of the Cretaceous
Period. These rocks crop out in relatively steep ridges in a narrow belt
around the margins of the White River Uplift. In the study area the youngest
rocks of this age form the Grand Hogback;

Younger Tertiary rocks of the Cenozoic Era are exposed in the Piceance Basin
west of the Grand Hogback. They comprise a sequence at least 5,000 feet thick
consisting in part of weak, variegated claystone, mudstone, and shale that
generally weathers to form broad valleys. The upper part of the sequence
consi sts of more resi stant dark marl stone and 1 i ght-col ored sandstone that
form plateaus, frequently terminating in sheer cliffs.

The youngest bedrock units in the region are the dark basalt flows and light
colored sediments of Tertiary age that uncomformably cap the higher elevations
in the northeast part of the White River Plateau. These rocks have a total
thickness of over 500 feet and are composed of several flows interbedded with
contemporaneous deposits of volcanic ash, sandstone and siltstone. Volcanic
plugs form the cores of several of the higher peaks in the region.

Quaternary
deposits.
along most

geology in the region is characteri zed by Pl ei stocence
Moraines representing several intervals of glaciation are
of the major valleys in the higher portions of the basin.

glacial
present
Severa 1

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