Continuing our ongoing mapping efforts along the Front Range Urban Corridor region of the state, this publication describes the geology of this 7.5-minute quadrangle containing the High Plains town of Greeley, Colorado and the agricultural lands to the north and east. Includes GIS data and two PDF plates. Digital ZIP download OF-20-05D
From the Geologic History:
The Greeley quadrangle lies in the northern part of the Colorado Piedmont. Like much of the piedmont, the quadrangle’s topography has relatively low relief (76 m difference between lowest and highest points), and natural exposures of bedrock and surficial units are rare except along stream banks. Quaternary deposits cover almost all the quadrangle and bedrock is exposed only at a few places, most being in the sumps of gravel pits. The present-day landscape of the Colorado Piedmont results from the down-cutting and geomorphic evolution of the South Platte River and Arkansas River drainage basins mainly during late Neogene and Quaternary time, beginning with removal of Paleogene and Neogene rocks and sediments that once covered the Upper Cretaceous strata in the basins (Madole, 1991). The predominant Quaternary deposits in the piedmont, including those in the Greeley quadrangle and surrounding area, are fluvial sediments of the South Platte River and its tributaries, and eolian sediments deflated from alluvium in these stream valleys and from upwind bedrock exposures in the piedmont (Madole, 1991; 2016). Most of the Greeley quadrangle is drained by the Cache la Poudre River and its south-flowing tributaries (Graham Seep, Eaton Draw, and Sand Creek); a smaller portion is drained by the South Platte River and its tributary Lone Creek. The Cache la Poudre River is a tributary of the South Platte River. The alluvial valleys of both of the major streams coalesce in the eastern part of the City of Greeley. The Cache la Poudre River valley is ~2.5 km wide at Greeley and trends northwest to southeast across the quadrangle. The South Platte River valley is ~3 km wide at Greeley and trends southwest to northeast near the southeast corner of the quadrangle.