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Field Division of Education
The Geology of Rocky Mountain National Park
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RecentAluvium, river gravels, soils, etc.
PleistoceneGlacial deposits

Nussbaum in part
PlioceneNussbaum in part

OligoceneWhite River
Denver, Dawson
EoceneArapaho, Raton (?)
Middle Park

Fox Hills
Lower CretaceousPurgatoire

Mississipiannot represented
Devoniannot represented
Siluriannot represented
OrdovicianFremont, Harding, Manitou
CambrianSawatch ss. and dolomite
Pre-CambrianBig Thompson schist and granites.

One region such as that within the borders of the Rocky Mountain National Park, contains a complete succession of the rocks formed during the entire geological time. Deposition during geological time seems to have predominated in certain areas of the earth at the expense of others. These areas of greater deposition seem to have been the lower portions of the continent, basin, or trough-like structures; and in them, sediments generally were accumulating. In order to accomodate the deposition of many thousands of feet of sediments which are known to have accumulated, the floor of the basin must have been sinking in relation to the surrounding areas which furnished the source of the detrital materials. These predominantly subsiding areas have been termed geosynclines. One of these, known as the Cordilleran geosyncline, is known to have occupied the site of the present Rocky Mountains extending from Mexico across parts of Arizona, New Mexico, Colorado, Utah, Wyoming, Idaho, Montana, Alberta and British Columbia, and northward across Eastern Alaska. When the continents were depressed in relation to sea level, the ocean waters entered these troughs, and if the continent was extensively depressed the waters spread beyond the margins of the geosynclines flooding the adjoining areas. At other times the continents were raised in relation to sea level and the ocean waters drained from them completely, usually lingering longest, however, in the geosynclines. During these times the surface of the newly formed deposits would be subject to erosion, and portions of the newly-formed sediments removed. Those sediments either were carried by the rivers beyond the margins of the continent, or some of the detrital material might be caught in the lower basins and valleys as aluvium, and stream and lake deposits. These subareal deposits, forming as they do above sea level, are known as continental deposits, in contrast to marine deposits, those formed in sea water.

Rocky Mountain National Park is located almost on the eastern border of the Cordilleran geosyncline; consequently marine waters spread over it repeatedly and thick sedimentary beds were deposited. Within the boundaries of the park almost nothing remains of the greater part of these formations with the exception of the very oldest. This region has been subject to great denudation during the later part of its history and the record has been largely destroyed. However, in the surrounding region, especially the foothill region immediately east of the park, most of the formations which formerly covered the rocks now seen in the park, are excellently represented. We may now take up briefly the more important events taking place in this region in past geologic time.

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