OF-18-01 Geologic Map of the Frederick Quadrangle, Weld and Broomfield Counties, Colorado


Extending previous CGS mapping efforts along the Front Range region of the state, this publication describes the geology of this 7.5-minute quadrangle located between Erie and Ft. Lupton, Colorado. The GIS data included in this package was brought into GeMS Level 3 compliance as of November 2022. Includes GIS data and two PDF plates. Digital ZIP download. OF-18-01D

From the Geologic History:

The Frederick quadrangle lies in the northern part of the Colorado Piedmont, near the axis of the Denver Basin and approximately midway along its length. Like much of the piedmont, the quadrangle has low relief (330 ft, 101 m). Quaternary deposits cover almost all its area and bedrock is exposed in only a few places. The Laramie Formation is the uppermost and youngest bedrock unit and underlies much of the Quaternary cover. It is a coal-bearing unit that was deposited in a low coastal-plain environment, on the west margin of the Cretaceous Interior Seaway during the Late Cretaceous (100-66 Mya). Oil and gas wells in the Berthoud quadrangle have penetrated underlying Cretaceous formations down to the Dakota Group (cross sections A-A’ and B-B’), but none of these formations are exposed in the quadrangle.

The present-day topography of the piedmont region results from evolution of the South Platte River and Arkansas River drainage basins during Quaternary time, beginning with removal of Paleogene and Neogene rocks that once covered the Upper Cretaceous strata. The dominant Quaternary deposits of the Colorado Piedmont in the Frederick quadrangle and surroundings are fluvial sediments of the South Platte River and its tributaries, and eolian sediments derived from these stream valleys and from bedrock exposures along the Piedmont. Northeast-flowing Little Dry Creek and Big Dry Creek drain most of the quadrangle and are tributaries to the South Platte River. In the northwest corner of the quadrangle there is an unnamed north-flowing tributary to St. Vrain Creek.