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<br />o
<br />...;r
<br />~ EXPLANA nON
<br />l\)
<br />
<br />_ QUA TERNARY and TERTIARY (QTuv)- Volcanic rocks
<br />
<br />_ TERTIARY (Tu)- {Browns Park and Troublesome Fonnutions)
<br />
<br />[]]I] TERTJARY lTI)- Uima, Green River. and Wasalch Fonnations
<br />
<br />~u TERTIARY and CRETACEOUS (TKI), (Middle Park Formation)
<br />
<br />8 TERTIARY and CRETACEOUS (TKv)- Laramide inlrusive rocks
<br />
<br />(:223 UPPER CRETACEOUS (Ku 1)- Mesaverde Group
<br />
<br />F. ^ .1 UPPER CRETACEOUS (Ku21' Mancos Shale, Pierre Shale, and (Colorado Group)
<br />
<br />m LOWER CRET ACF.OUS (KI)- Dakota Sandslone and Burro Canyon Fonnalion
<br />
<br />_ JURASSiC (1)- Morrison Formation and Entrada Sandslone
<br />
<br />~ LOWER JURASSIC and UPPER TRIASSIC (R)- Gle" Canyon Gruup, Wingate
<br />Sandstone, Chinle FomJation, (Chinle Fonnation)
<br />
<br />_ PERMIAN and PENNSYLVANIAN (PIP)- (Maroon, Belden, and Eagle Valley
<br />Fonnarions)
<br />
<br />~ MISSISSIPPIAN, DEVONIAN, ORDOVICIAN, and CAMBRIAN ROCKS
<br />(MDOE)- (Includes Leadville Limestone)
<br />
<br />.. PRECAMBRlAN (pE)- Igneous and metamorphic rocks
<br />
<br />NOTE.. STRATIGRAPHIC UNITS IN PARENTHESES DENOTE UNITS
<br />LOCATED IN THE SOUTHERN ROCKY MOUNTAINS AREA OF THE
<br />BASIN
<br />
<br />Figure 3. Generalized bedrock geology of the Upper Colorado River Basin study unit
<br />(modrtied from Schruben and others, 1974}-Continued,
<br />
<br />Dakota Sandstone composed of sandstones and shales;
<br />Mancos Shale; and Mesaverde Group, consisting of
<br />sandstone, shale, and coal. The Green River Formation
<br />of Tertiary age consists of siltstones, marlstones, sand-
<br />stones, limestones, and shales, Rocks of Tertiary and
<br />Quaternary age are present in the central pans of the
<br />subbasins and consist of predominantly continental
<br />sandstones, shales, coals, and locally abundant
<br />evaporite minerals, Tertiary volcanic rocks exposed in
<br />the study onit partially overlay or intrude many of the
<br />rocks described above,
<br />
<br />The highly variable geologic units of the study
<br />unit can be grouped together by the tectonic features
<br />present in the basin (fig, 4), These tectonic features
<br />
<br />represent variations in geology, which also reflect the
<br />differences in topography and climate in the study unit.
<br />The major tectonic features in the basin include the
<br />Gunnison Uplift, Sawatch Uplift, Middle Park Range,
<br />Sierra Madre Park Range, White River Uplift,
<br />Uncompahgre Uplift, and Piceance Structural Basin,
<br />which is considered the western extension of the Uinta
<br />Basin (Taylor and others, 1986),
<br />
<br />Geology is similar among the Gunnison Uplift,
<br />Sawatch Uplift, Middle Park Range, and Sierra Madre
<br />Park Range, In this area of the Southern Rocky Moun-
<br />tains prov ince, rocks of gneiss, schists, and granites of
<br />Precambrian age crop out and have been intruded by
<br />volcanic rocks, This area has been called the Colorado
<br />
<br />ENVIRONMENTAL SETTING 7
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