Qal
Recent alluvium
Holocene
Silty clay with local sands and gravels
Alluvial and floodplain deposits of smaller streams including Cheese Creek and Haines Branch. The
surface of these deposits is the modern floodplain and lies ~ 1 to 3 m above the present river level. The
upper portions of this unit are generally fine-grained sediment (silt and silty clay) that overlies varying
thicknesses of coarser sediment (sand and sand and gravel). Generally the overlying silty sediments are
less than 2 m thick. Qal alluvium directly overlies glacial sediment (primarily till) or Cretaceous
bedrock. Qal sediments may be inundated in large scale historic flood events.
Qal2
Higher alluvial deposits in larger stream valleys
Holocene to Latest Pleistocene
Silty clay with local sands and gravels
Abandoned alluvium of smaller streams including Cheese Creek and Haines Branch. The upper portion
of the Qal2 sediments lie 1 to 3 m above the Qal deposits. Sediments are generally less than 3 m thick,
and directly overlie glacial sediments (primarily till) or Cretaceous bedrock.
Qalt
Alluvial terraces in larger stream valleys
Late Pleistocene
Silt to silty clay
Higher older terraces of Cheese Creek, a tributary of Salt Creek. Terrace treads are ~10 m above modern
stream levels. Terrace treads are covered with ~4.5m of Peoria and Gilman Canyon Formation loess.
The treads are locally mantled with reworked reddish silty and clayey sediment that was derived from
Loveland loess that was deposited in alluvial fans or as slope wash. Terrace fills are mid to late
Pleistocene in age.
Qab1 Recent alluvium of the Big Blue River
Holocene
Clay to coarse sand
Recent alluvium and deposits along the floodplain of the Big Blue River. Most areas of Qab1 are
relatively small in area surrounding the deeply entrenched Big Blue River, or are located within recently
cut off meanders. Sediments on the flood plain are less than 3 m in thickness. Alluvial features are
distinctly visible on areas mapped as Qap1. These deposits may be inundated during large-scale flood
events. The Big Blue River was entrenched historically and the active channel lies 4 meters below the top
of the Qab1 sediments.
Qab1b Recent alluvium of the Big Blue River
Holocene
Clay to coarse sand
Areas of this unit lie 0.5-1.0 m higher than the Qab1 sediments. Sediments in this unit are less than 3
meters in thickness. Alluvial features are distinctly visible on the Qab1b surface, but are less apparent
when compared to alluvial features present on Qab1.
Qab2 Higher alluvium of the Big Blue River
Holocene
Clay to coarse sand
Older alluvium of the Big Blue River. The surface of these sediments are between 7 and 10 m above the
present river level. Sediments are generally 2-3 m thick and directly overlie glacial sediment. Few
alluvial features are visible on the surface of these deposits.
Qab3 Higher alluvium of the Big Blue River
Holocene to Latest Pleistocene
Clay to coarse sand
Older higher alluvium of the Big Blue River. Sediments are 1-3 m thick. Alluvial features are not
present on the Qab3 surfaces. Sediments are 13-16 m above the current river level. Some areas are
eroded by smaller tributaries of the Blue River, or are covered by small alluvial fan deposits sourced from
the adjacent uplands.
Qsw
Slope wash
Holocene
Clay to silt, with local sand to boulders.
Sediments located at the base of slopes. Generally, slope wash is sourced from adjacent loess or till.
Slope wash sourced from till contains a concentration of large boulders mixed with clay. Slope wash
deposits are generally less than 3 m thick and typically thin from their source.
Qp
Peoria Loess
Late Pleistocene
Silt to silty clay
Late Pleistocene aged loess. Loess is a wind-blown silt and clay deposit. Peoria Loess thickness ranges
from 1 to 8 m in the mapping area. Locally, some areas may be less than one meter in thickness near unit
boundaries and on steep slopes. Peoria Loess was likely deposited between ~ 25,000 and 14,000 years
ago. This unit is commonly underlain by Gilman Canyon Formation, a dark brown or black colored silty
loess unit that is ~1 meter in thickness.
Ql
Loveland Loess
Mid-Pleistocene
Silty clay to clayey silt.
Loveland Loess is older than the overlying Peoria Loess and Gilman Canyon Formation. Loveland Loess
can be distinguished from Peoria Loess by its characteristic red or pink color and finer (clay-rich) texture.
Some areas mapped as Loveland Loess along the western slope of the Big Blue River Valley contain
areas of reworked Loveland Loess mixed with older alluvial sands and gravels.
Qt
Sands
Pleistocene
Silty fine to coarse sands
Sandy sediments associated with Pre-Illinoisan glacial deposits. Sediments are likely Pre-Illinoisan
glacial outwash that has locally been modified by wind, probably in the late Pleistocene. Most exposures
of the upland sand are found on the eastern edges of stream valleys.
Qs
Glacial Till
Mid-Pleistocene
Clay with gravel
Tills in Nebraska were deposited by glaciers between ~ 2,500,000 and 600,000 years ago (Pre-Illinoisan
aged). Tills in the mapping area are generally reddish brown or bluish gray clay to silty clay with varying
amounts of gravels.
F
Fill
Built up areas where natural sediments are obscured, such as cities, gravel pits and dams.
W
Water