WSP00520

• File Number: 8059
• Description: Section D General Studies-State Water Plan
• State: CO
• Date: 1/1/1969
• Title: Writing the Report 1969-Environmental Conditions Draft
• Water Supply Pro - Doc Type: Report/Study

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DRAFT

order of age and their general distribution by major geographic sections

in the State.

(1) Precambrian Rocks - Very ancient rocks classed collectively

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as Precambrian or basement rocks made up large parts of the Front,

Park and Sawatch Ranges and are exposed also in other mountain

ranges and in the bottoms of many of the deep canyons in western

Colorado. In general, they are a mixture of metamorphic and

igneous rocks. The metamorphic rocks, which are the older,

are principally gneisses and schists of various kinds but include

subordinate quartzites, marbles, slates and phyllites. Intruded

into these oldest rocks are granites and related rocks of at least

three different ages within Precambrian time.

(2) Paleozoic Rocks - The Palcozoic Era is represented in Colorado

entirely by sedimentary rocks. Both the Great Plains and Plateau

Provinces are characterized by relatively undisturbed sedimentary

rocks. In the mountains, one major land area of late Paleozic time,

known as the Front Range Highland, occupied the site of most of the

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present Front Range, Wet Mountains, northern half of the Park Range ~
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and Middle Park. A second major land area, the Uncompahgre-San ~

Luis Highland, extended south-eastward from eastern Utah through

the Grand Junction vicinity, the San Juan Mountains, and the San

Luis Valley into New Mexico.

(3) Mesozoic Rocks - Mesozoic sedimcntary rocks, comprising those

of the Triassic, Jurassic, and Cretaceous Ages, are widely exposed

in Colorado. Through much of the State, they total more than

10,000 feet in thickness, and of this, the great bulk is Cretaceous

in age.

Thc Triassic rocks, less than 1,000 feet thick except near

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