OF-24-02 Geologic Map of the Timnath Quadrangle, Larimer and Weld Counties, Colorado

The purpose of this publication is to describe the geology, mineral and groundwater resources, and geologic hazards of the Timnath 7.5-minute quadrangle. It is a continuation of field mapping work in the northern Front Range and Colorado Piedmont areas where the CGS has mapped multiple quadrangles, this one covering the area around the town of Timnath. Nearby published quadrangles include Fort Collins, Severance, Loveland, Windsor, and Bracewell. CGS geologists Emily Perman, Alexander Marr, and Kassandra Lindsey completed the field work on this project during the mapping seasons of 2023-24. Digital ZIP download. OF-24-02D

From the abstract:

The Timnath 7.5’ quadrangle lies on the border of Larimer and Weld counties in northern Colorado. It includes the town of Timnath as well as portions of neighboring municipalities (Fort Collins, Severance, and Windsor) within its area. The topography is mostly subdued, with the highest points consisting of topographically inverted gravel deposits. This quadrangle is in a transitional zone between two geologic provinces: the Colorado Front Range and the Colorado Piedmont. The Front Range of the Rocky Mountains is characterized by areas of intense deformation resulting from several orogenies, and commonly the steeply dipping bedrock units form classic “hogback” structures along the range front. The Timnath quadrangle lies within the Denver Basin, an asymmetric, peripheral foreland basin, which formed during the Sevier and Laramide orogenies and set the stage for the transgression of the Mid-Interior Seaway (MIS). The quadrangle is entirely underlain by Cretaceous Pierre Shale, formed from marine sediments deposited when the continent’s interior was covered by the MIS. The Colorado Piedmont province is characterized by its relatively low topographic relief and overall lack of Neogene rocks, due to fluvial downcutting and erosion by the South Platte and Arkansas rivers and their tributaries. These river systems drain the Front Range and flow eastward into the Great Plains. The Quaternary history of the Timnath quadrangle is dominated by sediment deposition from two main sources: alluvial sediment from the Cache La Poudre River and its tributaries and eolian sediment sourced from the east. As a result of multiple episodes of aggradation and erosion in the river valley, this quadrangle hosts a sequence of fluvial terrace deposits, ranging in age from Holocene to Middle Pleistocene. Windblown sand mantles the upland northeast of the Cache la Poudre River valley and is re-worked by ephemeral stream channels and mass-movement processes. In some areas, the Timnath quadrangle is highly urbanized and in others it has remained mostly rural. Geologic hazards with potential to affect communities in this area include flooding, shallow groundwater, and expansive and (or) collapsible soils. At present, extraction of geologic resources (e.g., petroleum, gravel aggregate) in this quadrangle is generally low, but has seen greater volumes in the past.