OF-23-04 Geologic Map of the Milton Reservoir 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 over a dozen other quadrangles in the past several years. Completed CGS quadrangles in the immediate vicinity (to the north) are Milliken, La Salle, and Valley View School. CGS geologist Alex Marr completed the field work on this project during the 2022-23 mapping season. Digital ZIP download. OF-23-04D

From the abstract:

The Milton Reservoir 7.5-minute quadrangle is located in Weld County within the northern part of the Colorado Piedmont. The subdued landscape consists of gentle sloping uplands and the shallow valley of Beebe Draw, a north-south trending alluvial paleovalley where the ancestral South Platte River once flowed. The dominant surficial sediments in the quadrangle are Upper Pleistocene to Holocene eolian deposits where the sandier units form longitudinal and parabolic dune landforms, and the fine clay to silt rich units occur in interdunal valleys. Multiple alluvial deposits of different ages are scattered throughout the quadrangle. Early to Middle Pleistocene alluvial deposits as well as the eolian sediments mantle the uplands in the quadrangle. During the Middle Pleistocene, the ancestral South Platte River deposited alluvial sand and gravel in what is now called Beebe Draw. After its abandonment, additional Upper Pleistocene to Holocene alluvial deposits intermixed with mass wasting continued to be deposited in Beebe Draw followed by mantling of later eolian sediments. Although not well exposed, two bedrock units underlie the quadrangle: Lower Paleogene to Upper Cretaceous Denver Formation and Upper Cretaceous Laramie Formation. The dominant mineral resource is oil and gas followed by minor coal deposits, and potential sand and gravel. Groundwater is mostly sourced from alluvial deposits in Beebe Draw and the Laramie-Fox Hills bedrock aquifer. The dominant geologic hazards are expansive and collapsible soils as well as minor potential for flooding around the shores of Milton Reservoir.