Laserfiche WebLink
<br />DRAFT <br /> <br />. <br /> <br />the western edge of the State, resemble the late Paleozoic rocks, <br /> <br />both in character and distribution. The Jurassic rocks--principally <br /> <br />shale and sandstone--are more widespread because some of the <br /> <br />o <br /> <br />younger ones covered the old Front Range and the Uncompahgre <br /> <br />Highlands, but near the western border of the State they are <br /> <br />generally less than 1,000 feet thick. Most of the Triassic and <br /> <br />Jurassic rocks were deposited on land, as in shallow basins, or <br /> <br />along courses of sluggish rivers, or as sand dunes. In contrast, <br /> <br />most of the Cretaceous rocks were dcpositied in a vast inland sea <br /> <br />or in swamps along its shores. The sediments deposited in this sea <br /> <br />and related coastal swamp, mainly shale, sandstone, shaly limestone <br /> <br />and much coal, once formed a blanket 5,000 to 12,000 feet thick <br /> <br />over all of Colorado. <br /> <br />. <br /> <br />(4) Cenozoic Rocks - These rocks, the youngest unit of geologic <br /> <br />time, are partly clasti~ sedimentary rocks of continental origin <br /> <br />and partly igneous. These rocks accumulated principally near the <br /> <br />mountain borders and in the intermontane basins, and it is in <br /> <br />these areas that they are best seen today. At the same time that <br /> <br />~ <br />these. sedimentary rocks were accumulating, and continuing for some U) <br />~ <br />time afterward, intrusive rocks were emplaced in some parts of the ~ <br /> <br />mountain area. These intrusive rocks are important because many <br /> <br />kinds of ore deposits are related to them. During the latter part <br /> <br />of the early tertiary, when mountain building was drawing to a <br /> <br />close, thick deposits of fine-grained sediments accumulated in a <br /> <br />swampy lake that occupied an extensive basin in northwestern <br /> <br />. <br /> <br />Colorado and the adjoining parts of Utah and Wyoming. These <br /> <br />sediments now compose the Green River formation, which contains <br /> <br />Colorado's great deposits of oil shale. <br /> <br />.-16- . <br />