QalQuaternary alluvium of smaller streams (Holocene to modern)
Clayey silt, silt, sandy silt, and sand with very minor gravel.
Alluvium of lower-order streams the rolling loess uplands on either side of the North Loup River consists mostly of silt (reworked loess). In the valleys of larger streams, such as Davis, Wallace, and Fish creeks, alluvium consists of silt, sandy silt, silty sand, very fine to medium sand, and very minor gravel.
QaltQuaternary alluvium of terraces of smaller streams (Holocene to modern)
Clayey silt, silt, sandy silt, and sand with very minor gravel.
This mapping unit represents alluvium on terrace surfaces produced by the entrenchment of Davis, Wallace, and Fish creeks since Euramerican settlement ca. 1870, as well as any Holocene terraces.
Qanl1Historical alluvium of North Loup River (modern)
Light gray to very pale brown fine and medium sand.
This mapping unit represents very young alluvial terrain along the North Loup River. It includes alluvial bars, islands, and channels stabilized and accreted to the banks of that river since the time of the first aerial photographs of the area (1938).
Qanl2Older (distal) alluvium of North Loup River (Holocene)
Light gray to very pale brown fine and medium sand capped by a thin surficial soil of grayish brown to brown silty very fine to medium sand.
This mapping unit represents young alluvial terrain along the North Loup River. Areas mapped as this unit had already been accreted to the banks at the time of the first aerial photographs (1938). In 1938, these areas also exhibited relict channels and flood channels, some of which may still be discerned on modern orthophotographs. Areas mapped as Qanl2 are distinctly lower in elevation to areas mapped as Qanl3 (fill terrace) and, therefore, Qanl2 is younger and can be associated with post-terrace stream entrenchment and deposition.
Qanl3Old alluvial fill terrace of North Loup River (Late Pleistocene)
Light gray to very pale brown fine and medium sand capped by a thin surficial soil of grayish brown to brown silty very fine to medium sand.
This mapping unit represents the sediments of the low, broad alluvial terrace of the North Loup River, which is prominent on the east side of the river in the Scotia Quadrangle. The dominantly agricultural terrain atop this terrace is, with the exception of mapping unit Qes, significantly smoother than that associated with Qanl2. Aerial photographs from 1938 show faint remnants of channel-like features trending roughly southeastward across this terrace, but these features cannot be discerned in the most recent orthophotographs of the area, and they may have been destroyed by agricultural activities.
QfAlluvial fan deposits (Holocene to modern)
Brown, pale brown, and light yellowish brown silt and sandy silt.
A few, very small alluvial fans, each one less than 150 m in width, can be distinguished in aerial photographs in section 34 of T. 18 N., R. 12 W. These thin deposits consist of reworked Peoria Loess from adjacent uplands. Thin alluvial fan deposits may have been more common on valley slopes in the area than aerial photographs and ground reconnaissance indicate, in that such hypothetical deposits would have been amalgamated with in-place loess by agricultural practices after Euramerican settlement ca. 1870.
QesEolian sands (Holocene)
Light gray to very pale brown, well-sorted, fine to medium sand.
This mapping unit represents eolian sand reworked from underlying terrace deposits atop the fill terrace of the North Loup River. Small, subdued, vegetated dune forms 30-70 m in width are visible throughout this mapping unit in the earliest aerial photographs (1938), and some such features remain visible in modern orthophotographs, even though agricultural activities have obscured or obliterated others.
QpPeoria Loess (Late Pleistocene [Wisconsinan])
Laminated to massive, light brownish gray, pale brown, light yellowish brown, and brown silt and sandy silt.
The Peoria Loess is widespread in the mapped area, mantling essentially all of the uplands on either side of the North Loup River. In multiple outcrops near the river valley, it consists of coarse silt, and in some places it contains sandy lenses or laminae. Redoximorphic features and grayish colors are typically present at depth within the Peoria Loess. A borehole in the
subcircular basin of unknown origins in sections 17 and 18 of T.17 N., R. 12 W. exhibited at least two darker bands at depth within the Peoria Loess, and these bands are interpreted as paleosols. An alternate, but currently untestable, hypothesis is that the upper part of the loess sequence encountered in this borehole is actually incrementally deposited Holocene loess (cf. Mason and Kuzila, 2000). Extensive, low-angle (approximately north-dipping) laminae are exhibited by the Peoria Loess in a roadcut along 487th Road in the SW¼ NW¼ NW¼ of section 18 of T. 17 N., R. 12 W (Fig. 6). There is a minor component of dark brown loess-derived colluvium that merges with alluvium (Qal) on foot- and toeslopes of upland areas described by this mapping unit.
QlLoveland Loess (Middle Pleistocene [Illinoian])
Massive, pale brown, light yellowish brown, brown, and dark brown silt and clayey silt; locally sandy in lower part.
The Loveland Loess crops out only sparsely in the area of the Scotia Quadrangle, chiefly in the uplands west of the North Loup River. Remnants of buried hills eroded from the Loveland Loess can be seen in multiple deep roadcuts through the Peoria Loess in the Scotia Quadrangle (Fig. 1). It appears, therefore, that the Peoria Loess and Gilman Canyon Formation mantle a rolling paleolandscape eroded from the Loveland Loess during Wisconsinan times. The Sangamon Geosol is a prominent, blocky-structured, clay-enriched paleosol at the top of the Loveland Loess, and its presence in the Scotia area aids in the identification of the upper contact of the latter. In outcrops and in some cores, this paleosol, as well as much or all of the underlying part of the Loveland Loess, appears distinctly redder (7.5 YR hue) than the overlying Gilman Canyon Formation and Peoria Loess. This color contrast, however, is not present everywhere and in some boreholes the color contrast between the Loveland and Peoria loesses can be minimal. The lower contact of the Loveland Loess may be gradational into silty sands and sands, and brownish fine to medium sands may be present locally within the lower Loveland Loess.
NQsgSands and gravels (latest Neogene (?) and Early Pleistocene)
Cross-stratified and planar-laminated, medium to very coarse, white, very pale brown and light brown sands and granule to cobble gravels. Gravels consist of a mixture of crystalline clasts (including abundant granitic rock fragments and potassium feldspars) and locally-derived clasts of carbonate-cemented sandstone eroded from the Ogallala Group.
Thin sands and gravels appear beneath the regional loess sequence under the uplands (Figs. 7, 8). These sediments crop out very rarely atop the Ogallala Group. Small exposures around the shoreline of Davis Creek Reservoir have yielded an assemblage of mammalian fossils compatible with the late Blancan and IrvingtonianNorth American Land Mammal Ages (NALMAs), suggesting an Early Pleistocene, and possibly latest Pliocene, age. Souders (2000) discussed the presence of Pliocene alluvium in the enclosing area, implying an association with the Broadwater Formation. The existing age control on any such sediments in the surrounding area, however, is minimal, and prior age assignments, however uncertain, need to be reconsidered in the light of the revision of the Pliocene-Pleistocene boundary to 2.58 Ma by the International Union of Geological Sciences in 2009 (Gibbard et al., 2010).
NoUpper part of Ogallala Group (late Miocene)
Dominantly unconsolidated, well-sorted, white, light brownish gray, very pale brown, light brown, and pale yellow, very fine to medium sands with a distinct “salt and pepper” aspect due to the presence of dark mineral grains (friable, carbonate-cemented sandstones crop out locally or are rarely encountered in boreholes); fine, white rhizoliths are common in many sand and sandstone units; also contains rare, thin units of white, light olive brown sandy silt, silty sand, and silty very fine sandstone, as well as very rare, thin intraformational conglomerates containing clasts of authigenic carbonate and carbonate-cemented sandstone; white calcareous diatomite crops out in and around Happy Jack Peak in the Scotia Quandrangle and near Cotesfield, Nebraska, south-southeast of the mapped area.
Strata of the upper Ogallala Group (Figs. 7, 9) are exposed sparsely along the western valley wall of the North Loup River and Nebraska Highway 11 (e.g., NE¼ NW¼ SW¼ of section 35, SE¼ NW¼ SE¼ of section 27, NW¼ SW¼ of section 16, and SE¼SE¼ of section 6, T. 17 N., R. 12 W) and along Davis Creek (e.g., in the NW¼ SE¼ SW¼ of section 33, T. 17 N., R. 12 W) in the Scotia area. Joeckel et al. (2004) described the calcareous that were formerly mined at the base of Happy Jack Peak (NW¼ SW¼ of section 16, T. 17 N., R. 12 W.) in what is now known as the Happy Jack Mine (Fig. 9). In boreholes, the Ogallala Group can be distinguished from overlying sediments by virtue of its range of colors, the limited grain-size range and comparatively high degree of sorting of its constituent sands or sandstones, and the presence of rhizoliths.
According to Souders (2000), the Ogallala Group “cannot be subdivided consistently on the basis of subsurface data” in the larger geographic area of central Nebraska that includes the Scotia Quadrangle. We have not, therefore, differentiated it at the formation level in this map. Nevertheless, all available biostratigraphic evidence indicates that the sediments of the Ogallala Group cropping out in the area of the Scotia Quadrangle are of late Miocene age, corresponding to the Hemphillian NALMA, and therefore equivalent to the Ash Hollow Formation in western Nebraska (Joeckel and Tucker, 2013).
FFill
Artificial fill derived from local sources.
This mapping unit is intended to portray significant accumulations of artificial fill in dams, road embankments, and other manmade structures. Most of the artificial fill in the mapped area was derived from the Peoria Loess.
WWater