Geology and ground-water resources of the lower South Platte River valley between Hardin, Colorado, and Paxton, Nebraska: With a section on chemical quality of the ground water

Abstract

The study of the geology and ground-water resources of the lower South Platte River valley was made by the Ground Water Branch of the U. S. Geological Survey at the request of the U. S. Bureau of Reclamation and with the endorsement of the Colorado Water Conservation Board. The area includes parts of Colorado and Nebraska, covers about 3,200 square miles, and ranges in altitude from about 3,000 to 5,000 feet above sea level. The average annual precipitation in the area is about 16 inches and is sufficient to support grasses and some grains. Irrigation utilizing water diverted from the river and pumped from wells is extensively developed in the valleys of the South Platte River and its tributaries. The principal agricultural products are Corn, sugar beets, alfalfa, beans, wheat, barley, and livestock.The rocks exposed in the area are sedimentary and range in age from Late Cretaceous to Recent. The Pierre shale underlies the entire area. The Fox Hills sandstone and the Laramie formation underlie the western part and the Chadron, Brule, and Ogallala formations underlie the eastern part. Pleistocene arid Recent alluvium underlies the valleys of the South Platte River and its tributaries. The Pierre shale ranges in thickness from about 2,500 feet near Paxton, Nebr., to about 6,500 feet near Hardin, Colo., and yields water in small quantities to wells in the vicinity of Sterling, Colo. Within the area, both the Fox Hills sandstone and the Laramie formation range in thickness from a featheredge to nearly 200 feet and yield small quantities of water to stock and domestic wells. Although a test hole near Proctor, Colo., was drilled 102 feet into the Chadron formation, the total thickness of the formation was not ascertained; no wells within the area covered by this investigation are known to derive water from the formation. The Brule formation ranges in thickness from a featheredge to more than 500 feet and yields water to wells from fractured or porous zones. The Ogallala formation ranges in thickness from a featheredge near Sedgwick, Colo., to about 350 feet near Paxton, Nebr., and yields large quantities of water to wells. The alluvium ranges in thickness from a featheredge at the edges of valleys to about 300 feet in some places in the valleys. The alluvium occursin two physiographic forms Pleistocene and Recent terrace deposits and Recent floodplain deposits and yields abundant water to irrigation, public-supply, and other wells. Dune-sand deposits cover part of the area, range in thickness from a featheredge to about 100 feet, and yield water in small quantities to stock and domestic wells. Loess deposits cover much of the area and range in thickness from a featheredge to about 50 feet. Generally the loess is above the water table and is not known to yield water to wells.The principal source of ground water in the area is the alluvium of the South Platte River valley and of the tributary valleys of Lost,

Pleistocene and Holocene landscape development of the South Platte River Corridor, Northeastern Colorado

“…In addition, the maximum total width of the buried alluvial paleovalley, more than 13 km under the Orchard area (Berry and others, 2015a), is anomalously wide for a single paleovalley. These factors, combined with evidence in the drill hole data of deep paleochannels south of the modern South Platte River, indicate that the river was probably south of its present position along much of the reach between Masters and Fort Morgan at the time the Louviers Alluvium was deposited, but shifted back to the north during the late Pleistocene (Bjorklund and Brown, 1957;Gardner, 1967;Scott, 1978Scott, , 1982; Colorado Division of Water Resources, 2013). The Louviers level was most likely abandoned by incision before a return to net aggradation of the river system resulted in burial of the Louviers Alluvium by late Pleistocene Broadway Alluvium.…”

“…Primary and reworked deposits of Holocene and late Pleistocene eolian sand, and locally loess, cover much of the landscape, but stream and gully cuts, gravel pits, canal ditches, and road cuts provide local exposure of the fluvial deposits. Lithologic data from test holes, water wells, and oil and gas drill holes (Bjorklund and Brown, 1957; Colorado Division of Water Resources, 2013) provide information about buried deposits. Descriptions of the fluvial deposits included here are from the USGS geologic maps of the Orchard, Masters, Weldona, and Fort Morgan 7.5' Colorado quadrangles (Berry and others (2015a, b;2018b, c), and the supporting data release (Berry and others, 2018a).…”

“…Deposits of old alluvium (Qao) that could correlate to Rocky Flats Alluvium (Gardner, 1967;Scott, 1978Scott, , 1982 are mostly buried, but are exposed locally in gravel pits or inferred from drill hole data (Bjorklund and Brown, 1957;Colorado Division of Water Resources, 2013). The Qao deposits, which overlie Pierre Shale, form inferred terrace remnants roughly 60-70 m above the active floodplain others, 2015b, 2018c).…”

“…Deposits interpreted as Louviers Alluvium (Qlv) are not exposed in the study area but are inferred from lithologic data from test holes and water wells (Bjorklund and Brown, 1957;Gardner, 1967;Scott, 1978Scott, , 1982Colorado Division of Water Resources, 2013;Berry and others, 2015a, b). Evidence supporting their presence under younger deposits of late Pleistocene Broadway Alluvium includes maximum total thickness of alluvium overlying Pierre Shale, which locally is over 70 m where side-stream deposits from Kiowa and Bijou Creeks contribute to the total thickness, and up to 50 m where they do not.…”

“…The sidestream alluvium is more cohesive than the mainstream alluvium and forms a prominent bluff along the south side of the river. Based on bluff exposures and drill hole data from Bjorklund and Brown (1957) and the Colorado Division of Water Resources (2013), thicknesses of Broadway Alluvium could range from about 6-24 m for the sidestream deposits, and 12-30 m for the mainstream deposits.…”