P. R. Hanson, J. Bruihler and L. M. Howard
Mapping units
Qaf Alluvial fan deposits (Holocene)
Silt and sandy silt
Alluvial fan sediments are sourced from Peoria Loess (Qp) and are deposited on alluvium in the Qap_S3 unit. Sediments are generally thin, less than 2 m (6 ft) in thickness where mapped.
Qal Recent alluvium of small tributary valleys (Holocene to modern)
Sandy to silty deposits
Sediments deposited within small streams that are tributary to the North and South Platte Rivers. Most sediment in this mapping unit was deposited during the late Holocene. The deposits may be massive or thinly bedded. Sediments are generally less than 2 m (<~6.5 ft) thick, however some Qal sediments may locally be thicker.
Qap Alluvium of the Platte River system (late Holocene)
Sand and gravel, with local silty sediments
Qap_N1x and Qap_S1a deposits lie directly adjacent to the North and South Platte Rivers. Most land directly adjacent to the streams is vegetated with cottonwood and cedar and is primarily used for recreation and gravel mining. Sedimentary deposits are generally less than ~ 3 m (10 ft) in thickness overlying either older alluvium of the Platte Rivers.
Qap1_N1a Recent alluvium deposited by the North Platte River. Deposits have abundant bar and swale topography, and are flooded during flooding events. Areas covered by this unit are largely forested with cottonwood trees. This surface has variable relief and lies within ~ 1 m (1-3 ft) of the present level of the
North Platte River.
Qap1_N1b Deposits have more localized bar and swale topography, and are < 1 m (1-3 ft) higher than Qap1_N deposits. Areas covered by this unit are either forested with cottonwood trees or are used as pasture.
Qap1_N1c Deposits have more localized bar and swale topography, and are < 1m (1-3 ft) higher than Qap1_N deposits. Areas covered by this unit are typically in pasture or row crops.
Qap_S1a Recent alluvium deposited on the floodplain of the South Platte River.
Deposits have prevalent bar and swale topography, and are flooded during flooding events. Areas covered by this unit are largely forested. These surfaces lie approximately 1-2 m (3-7 ft) above the present river level.
Qap_N2 North Platte River Alluvium (middle to late Holocene).
Sand and gravel, with local silty sediments

Older alluvium of the North Platte River that is slightly higher (~ 0.5 to 1 m or 2-3 feet) above the modern floodplain than the younger alluvial deposits. Bar and swale topography is visible locally and the unit is extensively farmed. The upper 0.5-1 m (1.5-3 ft) is commonly silty overbank alluvial sediment with a poorly developed surface soil. Sand and gravel thickness varies, but commonly pale brown or calcium carbonate cemented very fine sand and silt of the Miocene aged Ogallala Group are encountered below depths of ~ 6 m (20 ft).
Qap_N3 North Platte River Alluvium (middle to late Holocene).
Sand and gravel, with local silty sediments
Older alluvium of the North Platte River with a surface that is 3-4 m (10-13 ft) above the Qap_N1a surface. Bar and swale topography is obscured and the unit is extensively farmed. The upper 0.5-1 m
(1.5-3 ft) is commonly silty overbank alluvial sediment with a poorly developed surface soil. The upper portion of this unit may contain varying amounts of eolian sand. Sand and gravel thickness varies, but commonly pale brown or calcium carbonate cemented very fine sand and silt of the Miocene aged
Ogallala Group are encountered below depths of ~ 6 m (20 ft).
Qap_S2a South Platte River Alluvium (middle to late Holocene).
Sand and gravel, with local silty sediments
Older alluvium of the South Platte River that is slightly higher (0.5-1 m or 2-3 ft) above the Qap_S1a surface. Bar and swale topography is only visible locally. This unit is extensively farmed. The upper
0.5-1 m (1.5-3 ft) is commonly silty overbank alluvial sediment with a poorly developed surface soil.
Sand and gravel thickness varies, but commonly pale brown or calcium carbonate cemented very fine sand and silt of the Miocene aged Ogallala Group are e
at depths below ~ 6 m (20 ft).
Qap-sr Sand Ridge (late Holocene) .
Fine to medium sand
Linear features that are composed predominantly of fine to medium sand. These units lie approximately
1.5 to 2.5 meters above the Qap_S2a surface.
Qap_S2b South Platte River Alluvium (middle to late Holocene).
Sand and gravel, with local silty sediments
Older alluvium of the South Platte River that is slightly higher (0.5-1 m or 2-3 ft) above the Qap_S1a surface. Bar and swale topography is not visible. This unit is farmed. This unit differs from Qap_S2a in that it has a pitted surface and saline soils. The upper 0.5-1 m (1.5-3 ft) is commonly silty overbank alluvial sediment with a poorly developed surface soil. Sand and gravel thickness varies, but commonly pale brown or calcium carbonate cemented very fine sand and silt of the Miocene aged Ogallala G
at depths below ~ 6 m (20 ft).
Qap_S3 South Platte River Alluvium (Holocene)
Sand and gravel, with local silty sediments
Deposits are about 0.5-1 m (2-3 ft) higher than Qap_S2 deposits.
Bar and swale topography is visible.
Land use is predominantly irrigated farmland or pastureland. Sand and gravel thickness varies, but

commonly pale brown or calcium carbonate cemented very fine sand and silt of the Miocene aged
Ogallala Group are encountered at depths below ~ 6 m (20 ft).
Qap_U1a Undifferentiated Platte River Alluvium (late Pleistocene)
Sand and gravel, with local silty sediments
Older slightly higher alluvium of the Platte River System that cannot be directly associated with either the
North or South Platte Rivers. The surface of this mapping unit lies ~ 5 m (17 ft) above the Qap_N1a surface. This unit is extensively farmed and is directly underlain by alluvium from the North or South
Platte Rivers and sediment of the Ogallala Group.
Qap_U1b Undifferentiated Platte River Alluvium (late Pleistocene)
Sand and gravel, with local silty sediments
Older slightly higher alluvium of the Platte River System that cannot be directly associated with either the
North or South Platte Rivers. The surface of this mapping unit lies ~ 3.5 m (11 ft) above the Qap_N1a surface. This unit is extensively farmed and is directly underlain by alluvium from the North or South
Platte Rivers and sediment of the Ogallala Group.
Qap_U1c Undifferentiated Platte River Alluvium (late Pleistocene)
Sand and gravel, with local silty sediments
Older slightly higher alluvium of the Platte River System that cannot be directly associated with either the
North or South Platte Rivers. The surface of this mapping unit lies ~ 4 m (13 ft) above the Qap_N1a surface. This unit occurs as isolated erosional remnants within the QAP_S2a surface. It is extensively farmed and is directly underlain by alluvium from the North or South Platte Rivers and sediment of the
Ogallala Group.
Qap_U1d Undifferentiated Platte River Alluvium (late Pleistocene)
Sand and gravel, with local silty sediments
Older slightly higher alluvium of the Platte River System that cannot be directly associated with either the
North or South Platte Rivers. The surface of this mapping unit is lower than the adjacent deposits and lies
~ 1-2 m (3-6 ft) above the Qap_N1a surface. This unit is extensively farmed and contains multiple gravel pits. It is directly underlain by alluvium from the North or South Platte Rivers and sediment of the
Ogallala Group.
Qes_ss Eolian sand sheet (Late Pleistocene/Holocene)
Fine sand
Windblown sand sheet deposits that have either less than ~ 3 m (10 ft) of topographic relief or few recognizable dune forms. The eolian sand for these sheets was sourced from the adjacent dunes to the northwest. Areas mapped as sand sheet are generally used as rangeland.
Qes_d Eolian dune sand (Late Pleistocene/Holocene)
Fine sand
Windblown dune sand deposits of the Nebraska Sand Hills, and dunes found on abandoned alluvial deposits of the North and South Platte Rivers and Birdwood Creek. The larger dunes have relief greater than 30 m (90 ft). In these dunes the sand is on average 15 m (50 ft) thick and overlies

Pliocene/Pleistocene age alluvial deposits or Ogallala Group sandstone. Studies have shown the dunes in the Nebraska Sand Hills were most recently active ~800 years ago (Goble et al., 2004; Mason et al., 2004;
Loope and Swinehart, 2000). Although no numerical ages were taken from dunes on the map, the dunes are likely late Pleistocene to early Holocene in age. Areas mapped as dune sand are generally rangeland and to a lesser extent irrigated agricultural cropland.
Qp Peoria Loess (Quaternary)
Silt and sandy silt
Yellowish brown to yellowish gray silt and sandy silt present on uplands to the south of the South Platte
River. Peoria Loess is a wind-blown silt that lies on alluvium deposited prior to 14,000 years ago by the
Platte River. The Peoria Loess which is up to 50 meters (164 ft) thick in the region was deposited between ~ 25,000 to 14,000 years ago (Bettis et al., 2003). Peoria Loess is ~3.6 meters (12 ft) thick and directly overlies sand and gravel deposited by the Platte River system. Dunes may be present locally under the loess. The sand and gravel is approximately 5.5 meters (18 ft) thick and directly overlies silts and sands of the Ogallala Group.
W Water
P Pit