Geologic map of the Masters 7.5' quadrangle, Weld and Morgan Counties, Colorado

Scientific Investigations Map 3344
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Abstract

The Masters 7.5' quadrangle is located along the South Platte River corridor on the semiarid plains of eastern Colorado and contains surficial deposits that record alluvial, eolian, and hillslope processes that have operated in concert with environmental changes from Pleistocene to present time. The South Platte River, originating high in the Colorado Front Range, has played a major role in shaping the surficial geology of the quadrangle, which is situated downstream of where the last of the major headwater tributaries (St. Vrain, Big Thompson, and Cache la Poudre) join the river. Recurrent glaciation (and deglaciation) of basin headwaters affected river discharge and sediment supply far downstream, influencing deposition of alluvium and terrace formation in the Masters quadrangle. Kiowa and Bijou Creeks, unglaciated tributaries originating in the Colorado Piedmont east of the Front Range and joining the South Platte River just downstream of the Masters quadrangle, also have played a major role by periodically delivering large volumes of sediment to the river during flood events, which may have temporarily dammed the river. Eolian sand deposits of the Greeley (north of river) and Fort Morgan (south of river) dune fields cover much of the quadrangle and record past episodes of sand mobilization during times of prolonged drought. With the onset of irrigation and damming during historical times, the South Platte River has changed from a broad, shallow sandy braided river with highly seasonal discharge to a much narrower, deeper river with braided-meandering transition morphology and more uniform discharge. Along the reach of river in the Masters quadrangle, the river has incised into Upper Cretaceous Pierre Shale, which, although buried by alluvial deposits here, is locally exposed downstream along the South Platte River bluff near the Bijou Creek confluence, in some of the larger draws, and along Wildcat Creek.

Suggested Citation

Berry, M.E., Slate, J.L., Paces, J.B., Hanson, P.R., and Brandt, T.R., 2015, Geologic Map of the Masters 7.5' Quadrangle, Weld and Morgan Counties, Colorado: U.S. Geological Survey Scientific Investigations Map 3344, 10 p. appendix, 1 sheet, 1:24,000, http://dx.doi.org/10.3133/sim3344.

ISSN: 2329-132X (online)

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Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Geologic map of the Masters 7.5' quadrangle, Weld and Morgan Counties, Colorado
Series title Scientific Investigations Map
Series number 3344
DOI 10.3133/sim3344
Year Published 2015
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Geosciences and Environmental Change Science Center
Description Sheet: 53.82 x 35.65 inches; Appendix; Database Files; Read Me
Country United States
State Colorado
County Morgan County, Weld County
Online Only (Y/N) Y
Additional Online Files (Y/N) Y