OF-21-04 Geologic Map of the Hardin Quadrangle, Weld County, Colorado


The purpose of this report is to describe the geology, geologic resources and geologic hazards of this 7.5-minute quadrangle located along the northern Front Range of Colorado. CGS geologists Martin Palkovic and Matt Morgan completed the field work on this project during the fall of 2020 through the spring of 2021. Digital ZIP download. OF-21-04D

From the Geologic History:

The Hardin quadrangle lies in northeastern Colorado, approximately 76 km northeast of metropolitan Denver and approximately 22 km southeast of Greeley. The quadrangle is located within the Colorado Piedmont section of the Great Plains physiographic province, an area in eastern Colorado where Neogene rocks were removed by erosion. The Colorado Piedmont is bounded by the Front Range foothills to the west, the High Plains to the east and north, and the Raton Basin to the south. Two regionally extensive unconformities may define the onset of Piedmont deformation and uplift in eastern Colorado: a late Eocene unconformity concurrent with the end of the Laramide orogeny, and an early Miocene unconformity that separates the Ogallala Formation from older strata below. In eastern Colorado, Late Cretaceous (100-66 Ma) marine sediments were deposited during transgressive and regressive episodes of the Western Interior Seaway (WIS), a large epeiric sea that existed during the Late Cretaceous. The beginning of the Laramide orogeny at ~70 Ma is roughly contemporaneous with the final regression of the WIS in eastern Colorado. This final regressive pulse of the WIS is responsible for the deposition of the Niobrara Formation, Pierre Shale, Fox Hills Sandstone, and Laramie Formation. These bedrock units commonly underlie unconsolidated sedimentary material east of Greeley. As the Laramide orogeny progressed, sediments eroded off of the uplifting Rocky Mountains, filling the down warped foreland basin from west to east with detrital sediment. This sedimentary basin , known as the Denver Basin, is a strongly asymmetric structural basin, with steeply dipping strata along its western flank and gently dipping strata along its eastern flank.

NOTE: Starting with this geological Statemap publication, we are implementing USGS Geologic Map Schema Standard (GeMS 3) data standards. Please refer to the enclosed OF-21-04 Read_Me file for details on the structure of what is included with the map.