OF-20-06 Geologic Map of the Kersey Quadrangle, Weld County, Colorado


The purpose of this publication is to describe the geology, geologic resources, and geologic hazards of this 7.5-minute quadrangle. It is a continuation of field mapping work on the northern Front Range of Colorado where the CGS has cumulatively mapped 10 other quadrangles, this one extending the contiguously mapped area further east into the High Plains. CGS Geologists Kassandra Lindsey and Martin Palkovic completed the field work on this project during the mapping seasons of 2019-2020. Digital ZIP download. OF-20-06D

From the Geologic History:

The Kersey quadrangle is located approximately 80 km northeast of Denver and 40 km east of Fort Collins, Colorado. The map area lies within the Colorado Piedmont section of the Great Plains physiographic province. In eastern Colorado, Upper Cretaceous rocks are the predominant bedrock units and were deposited during the transgressive and regressive stages of the Western Interior Seaway (WIS). The Laramide orogeny began at around 70 Ma and corresponds with the final stages of the WIS in eastern Colorado. It was during this time that the sediments forming the major bedrock units, identified in oil and gas well logs within the map area were deposited: Carlile Shale, Greenhorn Limestone, and Codell Sandstone (collectively known as the Colorado Group, unit Kcgg), Niobrara Formation (unit Kn), and Pierre Shale (unit Kp). However, bedrock units are not exposed within the Kersey quadrangle because they are mantled by surficial deposits. As the Laramide orogeny progressed, the Denver Basin was created with steeply dipping bedrock on the western margin, and dip angles decrease significantly toward the east.