OF-24-03 Geologic Map of the Severance Quadrangle, Weld County, Colorado

The purpose of this publication is to describe the geology, mineral and groundwater resources, and geologic hazards of the Severance 7.5-minute quadrangle. It is a continuation of field mapping work in the northern Colorado Piedmont where the CGS has mapped multiple quadrangles, this one covering the area around the town of Severance. Nearby published quadrangles include Timnath, Windsor, Bracewell, Greeley and Fort Collins. CGS geologists Alexander Marr, Emily Perman and Kassandra Lindsey completed the field work on this project during the mapping seasons of 2023-24. Digital ZIP download. OF-24-03D

From the abstract:

The Severance 7.5-minute quadrangle in Weld County lies within the northern Colorado Piedmont. Uplands in the northern part of the mapped area are underlain by bedrock and Middle Pleistocene gravel deposits. Ancient tributaries of the Cache la Poudre River—The Slough, Coalbank Creek, and the “Eaton” paleovalley—drain southward from these uplands, incising the terrain, and creating the gently sloping terrain in the southern part of the mapped area. Holocene to Late Pleistocene eolian sand and silt/clay, locally mixed with bedrock residuum, comprise the majority of Quaternary surficial deposits. Alluvial units of varying ages were episodically deposited from the Middle Pleistocene to the Holocene. Colluvium and sheetwash deposits mantle valley margins and bedrock slopes in the northern part of the quadrangle. The Upper Cretaceous Pierre Shale, Fox Hills Sandstone, and Laramie Formation comprise the bedrock units in the quadrangle. A localized Cenozoic conglomeritic sandstone crops out along Black Hollow Reservoir. Subsurface Laramide-age deformation produced the concealed Windsor Wrench Fault Zone and associated folds. Oil and gas, sourced from the Cretaceous marine sedimentary rocks including the Niobrara Formation, Codell Sandstone, and Pierre Shale, are the most prevalent natural resources. Minor sand and gravel, and potential coal and uranium resources are also present. Groundwater is derived from the Laramie–Fox Hills and Upper Pierre aquifers, as well as from alluvial and eolian deposits. Principal geologic hazards include expansive and collapsible soils, localized flooding and debris flows in the modern valleys, and minor induced seismicity from wastewater injection.