Geologic Formations and Their Water-bearing Properties
Quaternary System--Pleistocene SeriesUndifferentiated Deposits
Deposits of gravel, sand, silt, and clay overlie the Ogallala formation and although somewhat similar lithologically to the Ogallala formation, they are of Pleistocene age. It has not been practicable to subdivide these deposits into smaller units, so they are referred to as undifferentiated Pleistocene deposits.
Character--The undifferentiated Pleistocene deposits consist principally of unconsolidated gravel, sand, silt, and clay. Sand and gravel are the most abundant materials and silt and clay occur in lesser amounts but locally may be the predominant constituents. The coarse sand and the gravel are composed of quartz, feldspar, and other material derived from igneous rock. Water-worn pebbles of caliche derived from the Ogallala formation are common in these deposits, particularly in the lower part near the contact between these deposits and the underlying Ogallala formation. In places where the Ogallala formation is relatively thin or absent, water-worn pebbles of materials derived from rocks of Cretaceous age, principally from the Niobrara formation, are scattered through the deposits.
The Pleistocene deposits are poorly sorted and very lenticular. Individual beds are discontinuous and may grade laterally or vertically from one lithologic type to another within relatively short distances. Interbedded with the sands and gravels are many lenses of silt, sandy clay, and clay. Clay in the form of rounded "clay balls" that range in diameter from a few inches to more than a foot are interspersed throughout the deposits. These deposits are for the most part unconsolidated. Some beds, however, are cemented by calcium carbonate to form hard "mortar beds" resembling concrete, a notable example being the cemented deposits occurring along the south bank of Beaver (Ladder) Creek, just above the water surface, at a point just below the bridge in the NW 1/4 SW 1/4 sec. 21, T. 17 S., R. 33 W.
The undifferentiated Pleistocene deposits include the terrace deposits of Beaver (Ladder) Creek valley which are composed mainly of gravel containing intermixed sand, silt, and clay. The sand and gravel is composed principally of material derived from igneous rocks. The terrace deposits are patchy in character and occur as isolated terrace remnants of channel deposits that were formerly much more extensive. Downcutting by Beaver Creek was responsible for the removal of most of the channel deposits, leaving scattered isolated remnants along the valley sides. The terrace deposits are of commercial importance and are the source of sand and gravel used for construction materials locally. The Geist (Christy) gravel pit, situated in the NE 1/4 SW 1/4 sec. 21, T. 17 S., R. 33 W., has been in operation intermittently for several years and large amounts of gravel and sand have been removed for construction purposes. Although not used in 1940 as extensively as the Geist (Christy) pit, two other gravel pits have been operated on terrace deposits along Beaver (Ladder) Creek valley - the Garvin gravel pit, situated on the section line between secs. 22 and 23, T. 17 S., R. 34 W. about a quarter of a mile south of the north section line, and the Gilbert Lenz gravel pit, situated in the SE 1/4 NW 1/4 sec. 22, T. 17 S., R. 34 W. The sand and gravel deposits at the Garvin pit are about 15 feet thick according to a measurement of the south vertical face of the workings in 1940. Similarly, the deposits of sand and gravel at the Lenz pit were from 15 to 18 feet in thickness in 1940, the deposits consisting of crossbedded sand and gravel interspersed with green clay balls and water-worn pebbles of white Ogallala caliche material. A fourth gravel pit was also visited in the SW 1/4 SE 1/4 sec. 15, T. 17 S., R. 33 W. The deposits occurred as a terrace remnant on the west side of Beaver (Ladder) Creek and there was evidence that the pit has been worked extensively.
The finer materials of the Pleistocene deposits consist of clay and silt. Clay was encountered in about half of the 23 test holes (1, 5, 10, 13, 15, 16, 17, and 19-23 incl.) drilled in Scott County. The clay ranges from silty to sandy and is tan, blue gray, light gray, dark gray, yellow gray, light greenish gray, pale green, brown, yellow, pinkish, and black. The individual beds range in thickness from 1.5 to 50 feet. Many of the clay beds contain small invertebrate fossils.
Lenses of silt and sandy silt ranging in thickness from about 1.5 to 68 feet were penetrated in test drilling. Beds of silt were encountered throughout the entire vertical range of the Pleistocene deposits in Scott County. The silt is tan, brown, yellow .tan, grayish tan, light gray, gray, light green gray, yellow gray, and pinkish brown. Some of the silt layers are calcareous and are white to light gray in color.
The sands in the Pleistocene deposits are generally poorly sorted and range in texture from very fine- to coarse-grained and often contain a few pebbles. Fine to very coarse gravels make up the coarser sediments of the Pleistocene. Lenses of intermixed sand and gravel are common. The thickness of most of the sand and gravel lenses encountered in test holes ranges from a few feet to 21 feet. Test hole 22 in southern Scott County penetrated 21 feet of sand and medium to fine gravel between depths of 67 and 88 feet.
The upper part of the undifferentiated Pleistocene deposits is well exposed in two gravel pits - one about 1.5 miles north and 1 mile west of Scott City in the NW 1/4 SW 1/4 sec. 12, T. 18 S., R. 33 W., and the other about 1 mile east of Shallow Water in the SE 1/4 sec. 30, T. 19 S., R. 32 W. The deposits of sand and gravel in these two gravel pits are lithologically similar and contain intermixed silt and clay and scattered clay balls.
Distribution and thickness--Pleistocene deposits are present nearly everywhere in Scott County except in the northern part where tributary streams have removed them and exposed Pliocene and Cretaceous rocks. In most places they are covered with a mantle of loess of variable thickness, and in the southeastern part of the county they are covered by dune sand.
The thickness of the Pleistocene deposits ranges from a few feet to 196 feet. The maximum thickness in this area was encountered in test holes 17 and 19 in south-central Scott County near Shallow Water, where 196 feet of sediments of Pleistocene age were penetrated in each of the test holes. These test holes were drilled in what is believed to be the deepest part of the buried trough in Scott County. Test hole 13, drilled near the terminus of Whitewoman Creek where the creek loses its identity and merges with the Scott Basin, penetrated 190 feet of undifferentiated Pleistocene deposits. Test hole 16, drilled about 2 miles east of Shallow Water, penetrated 168 feet of Pleistocene deposits. The Pleistocene deposits thin eastward and westward from the vicinity of the buried trough whose course is revealed by the contours showing the configuration of the pre-Tertiary bedrock surface in Figure 2.
Origin--Most of the materials in the undifferentiated Pleistocene deposits represent channel and floodplain sediments that were laid down in much the same manner as the stream-laid deposits of the Ogallala formation. The sediments that were deposited in the deepest part of the buried trough were the result of channel filling by an ancestral stream that formerly occupied the north-south-trending trough whose axis passed near Scott City and Shallow Water and extended southward into Finney County. The trough was cut to its maximum depth early in the Pleistocene after which a period of alluviation or perhaps several successive periods of channel filling resulted in the great thickness of undifferentiated Pleistocene deposits in the buried trough. The origin of the Pleistocene deposits occurring as terrace remnants along the valley sides of Beaver (Ladder) Creek in the northwestern quarter of the county have been discussed in the section on Geology - Quaternary Period.
Age and correlation--Fossils collected from these deposits in Scott County indicate that they are of Pleistocene age. Fossil material collected in 1939 from two gravel pits in Scott County by H. T. U. Smith has been identified by Claude W. Hibbard. Six teeth that were collected by Smith from the Geist (Christy) pit, located about 5 miles north and 3.5 miles west of Scott City, were identified by Hibbard as Bison bison. Fossil material collected by Smith from the gravel pit located about 1 mile east of Shallow Water was identified by Hibbard as Bison bison material.
A crew of W.P.A. workmen at the Geist (Christy) gravel pit unearthed two large fossil horns in February and March 1939. The two horns, together with a skull that was found later, were mounted and placed on display in the Ford Garage in Scott City. These horns measured 72 inches from tip to tip. This specimen was identified by Hibbard from a photograph as Superbison latifrons (Pl. 15A).
Plate 15--Vertebrate fossils collected from gravel pits along Beaver (Ladder) Creek in Scott County. A, Skull of Superbison latifrons. B and C, Top and side views, respectively, of lower molar (M3) of Paraelephas cf. columbi, D and E, Top and side views, respectively, of upper molar of Paraelephas cf. columbi, F and G, Top and side views, respectively, of upper premolar of Paraelephas cf. columbi. A larger version of this photo is available.
Fragmentary teeth collected by me in 1940 from the Gilbert Lenz gravel pit in the SW 1/4 NE 1/2 sec. 22, T. 17 S., R. 34 W. were subsequently identified by Hibbard as Procamelus, a Tertiary form. A fragment of a horse tooth, either Pliohippus or Hipparion was also identified. Because of the fragmentary condition of the material, exact identification was not possible.
The undifferentiated Pleistocene deposits have also yielded invertebrate fossils. Mollusks recovered from several of the test holes drilled in Scott County are listed below. Identifications were made by A. B. Leonard.
Mr. Leonard reported that all of these forms seemed to be well fossilized, but pointed out that fossilization in snails is sometimes very difficult to determine with accuracy. He also reported that Vallonia and Succinea exist in this part of Kansas today and therefore cannot be used to identify Pleistocene deposits.
The invertebrate fossils collected from the undifferentiated deposits in Scott County are additional evidence indicating Pleistocene age for these beds. Many of the mollusks given in the preceding list are identical with forms found in the Meade formation of Meade County (Frye and Hibbard, 1941, pp. 413-415) where they are associated with Pleistocene vertebrates. Similar invertebrate fossils were recovered from several of the test holes drilled in Finney and Gray counties (Latta, 1944, p. 175). Latta also called attention to similar forms collected by Thad G. McLaughlin from a bed of silty clay in the SE 1/4 NE 1/4 sec. 3, T. 27 S., R. 31 W., in the northeastern corner of Haskell County.
The presence of water-worn caliche and "mortar bed" pebbles also indicate Pleistocene age for these deposits in Scott County. As has been pointed out earlier, water-worn fragments of Ogallala material are common in the Pleistocene gravels.
Water supply--Many of the wells in the Scott Basin derive water from the undifferentiated Pleistocene deposits. Some wells penetrate these deposits as well as the water-bearing section of the Ogallala formation below and may obtain water from both sources. The terrace deposits found in isolated patches along the valley sides of Beaver (Ladder) Creek in the northwestern quarter of the county are relatively permeable but generally occur above the water table and are therefore not important as a source of water in that vicinity.
The yields of wells in the undifferentiated Pleistocene deposits range from several gallons a minute from small domestic and stock wells to more than 1,000 gallons a minute from some of the large irrigation wells. Where wells penetrate the Pleistocene deposits and the water-bearing beds in the underlying Ogallala formation, it is practically impossible to determine the quantity of water being furnished from each of the two sources. The thickness of saturated material in the Pleistocene deposits differs greatly, as shown by the profile sections in Figure 5. Logs of test holes show that a large percentage of the saturated zone in these deposits is composed of sand and gravel, so the amount of water available is believed to be 1arge.
Six samples of water were collected from wells (107, composite sample from 82 and 112, 174, 236, 252, and 262) obtaining water from undifferentiated Pleistocene deposits and/or the underlying water-bearing beds in the Ogallala formation. All of the wells were situated in the Scott Basin, in the vicinity of the deep buried trough where maximum thicknesses of Pleistocene deposits occur. The total dissolved solids in the six samples ranged from 205 to 563 parts per million, two of the samples (wells 174 and 236) having 563 and 536 parts respectively of total dissolved solids. The total hardness ranged from 172 to 344 parts per million and averaged 238 parts. The iron content in the six samples ranged from 0 to 3.3 parts per million, and the fluoride content ranged from 1.0 to 2.7 parts per million, four of the samples (wells 107, 236, 252, and 262) having 1 part or more of fluoride, and two samples (composite of wells 82 and 112, and 174) having 2.0 and 2.7 parts per million of fluoride, respectively. The sulfate content in all six samples showed a greater range in concentration - four of the six samples (wells 107, composite sample of 82 and 112, 252, and 262) had a sulfate content ranging from 26 to 41 parts per million. Samples of water from wells 174 and 236 had sulfate contents of 194 and 145 parts per million, respectively. The fluoride content in some of the water derived from the undifferentiated Pleistocene deposits and/or the water-bearing beds of the underlying Ogallala formation is relatively high. The composite sample collected from the public supply at Scott City (wells 82 and 112) at a time when both wells were pumping had a fluoride content of 2.0 parts per million.
The analyses of these six samples of water from the undifferentiated Pleistocene deposits and/or Ogallala formation in Scott County indicate that the water is well within the safe limits for use in irrigation according to the principles discussed by Scofield (1933).
Quaternary System--Pleistocene and Recent SeriesLoess
A relatively thin deposit of loess overlies the undifferentiated Pleistocene deposits in much of Scott County. In places where the undifferentiated Pleistocene deposits are absent the loess may rest directly on the Ogallala formation. The loess is exposed in road and highway cuts in the northern half of the county; typical exposures of loess are shown in Plate 16. The loess is generally light buff to light brown but may grade upward into a darker brown to black soil zone at the top. The material is structureless and lacks bedding. Exposures of loess in road cuts are typical in appearance to loess found elsewhere, except that vertical parting may be less prominent. In places it contains small, scattered concretionary nodules of lime carbonate. It is composed principally of silt but contains some very fine sand. Mechanical analyses made by Smith (1940, p. 122) included analyses of two samples of loess (11 and 12) collected from road cuts near the north county line in northern Finney County. One sample was collected in the northwest corner of Finney County in the NW 1/4 sec. 6, T. 21 S., R. 34 W., and the other in the NE 1/4 sec. 2, T. 21 S., R. 29 W., near the Lane-Finney County line. These analyses (Table 17) indicated maxima in the 0.062-0.031 mm division. Fractions larger than 0.062 mm were separated by screening; those smaller than 0.062 mm were separated by the pipette method.
Table 17--Mechanical analyses of loess and associated materials. Modified from Smith (1940, p. 122).
Natural exposures of loess are relatively few and small because of the incoherent character of the material. Because road cuts and other excavations are generally shallow, the complete thickness of the loess is not readily determinable and the irregularities of the buried pre-loess surface are concealed. It is estimated that the thickness of the loess in Scott County ranges from a few feet to about 30 feet. Most of the test holes in Scott County encountered deposits of loess that ranged in thickness from 5 to 28 feet. The maximum thickness was encountered in test hole 3. Gastropod shells were collected from an exposure of loess in an abandoned railroad cut in the northern part of the county in the NE 1/4 NE 1/4 sec. 36, T. 16 S., R. 33 W. (Pl. 16A). Gastropod shells and fragments of pelecypod shells were recovered from the upper part of most of the test holes drilled in Scott County, some of which came from the upper loessial part of the test holes.
Plate 16--A, Typical loess exposed in abandoned railroad cut near the NE cor. sec. 36, T. 16 S., R. 33 W.; B, loess exposed on east side of freshly graded road in the SW cor. NW NW sec. 17, T. 16 S., R. 33 W.
The age of the loess can be stated only in relative terms, for as A. B. Leonard has pointed out, the fossilization of snails is sometimes very difficult to determine with accuracy, and some of the forms are of doubtful value because they exist in western Kansas today. At least in part, the loess probably belongs somewhere in the upper Pleistocene and may grade imperceptibly upward into loess of Recent age. It is younger than volcanic ash, and older than dune sand at the few localities where it is found in contact with one or the other of these, according to Smith (1940, pp. 124-125). He also suggests that it may be contemporaneous with and in part grade laterally into the Kingsdown formation. More than one age of loess may be present in Scott County, but no attempt was made to subdivide it. The loess lies above the water table in Scott County; hence, it furnishes no water to wells.
Dune sand of Quaternary age occurs in an area of approximately 9 square miles in the southeastern corner of Scott County and in smaller scattered areas in the southeastern part of the county (Pl. 1). The dune sand is composed predominantly of uniform fine-to medium-grained well-rounded quartz sand and contains smaller amounts of silt and clay. The sand has been accumulated by the wind to form small hills and ridges. The exact thickness of this material in Scott County has not been determined, but it is believed that the dune sand mantle ranges in thickness from a few feet to perhaps as much as 50 feet. In places the soil zone is thin and attempts at cultivation have stripped the protective vegetative cover allowing the upper surface to be subjected to renewed wind action. The dune sand probably was derived from the denudation of nearby Pliocene and Pleistocene deposits. Smith (1940, pp. 127-128; 153-168) gives a detailed discussion of the origin of sand dunes in western Kansas.
No wells obtain water directly from the dune sand in Scott County, for it is everywhere above the water table, but sand dunes serve as valuable intake areas for ground-water recharge from local precipitation because the porous materials comprising them are highly permeable and permit infiltration readily.
Alluvium of late Quaternary age is found in Beaver (Ladder) Creek valley in Scott County (Pl. 1). Some of the tributary streams in the extreme northern part of the county are still in the process of downcutting so that there is little or no alluvium along the greater part of their courses in Scott County. Where present, the alluvium is thin and occurs as very narrow bands along the northern part of their present channels; accordingly, it is not shown on the geologic maps.
The character of the alluvium in Beaver Valley is typical of stream-laid deposits and ranges in texture from silt to sand and coarse gravel. The youngest deposits consist largely of sand and silt deposited over the floodplain in time of flood or in normal conditions in the channel of the stream. Beneath the finer surface deposits are layers of sand and gravel slightly older but of similar origin. The alluvium grades into the terrace deposits, so the lower part of the valley fill in some places is of late Pleistocene age and represents the basal part of a cut and fill terrace deposit.
The alluvium is underlain by the Ogallala formation in most parts of Beaver Creek Valley, but in the vicinity of Scott County State Park the alluvium rests uncomformably on the Niobrara formation. Scanty data indicate that the thickness of the alluvium along Beaver Valley ranges from a few feet to an estimated maximum of about 20 feet. The yields of wells tapping the alluvium in Beaver Valley generally are adequate for domestic and livestock purposes.
The analysis of one sample of water (3) collected from a well in shallow alluvium of a tributary drainage in the northeastern part of the county in the SW 1/4 NW 1/4 sec. 4, T. 16 S., R. 31 W. showed dissolved solids, 462 parts per million; total hardness, 394 parts; sulfate, 171 parts; fluoride, 1.0 part; and iron, 2.1 parts. The well from which the water was collected is in an area in which the Niobrara formation is at or near the surface and the chemical quality of the water in the alluvium in that vicinity is doubtless affected somewhat by the underlying chalk of that formation.
Kansas Geological Survey, Scott County Geohydrology|
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Web version March 2003. Original publication date July 1947.