Plate 1 is an areal geologic map of Elk County. Stream valley alluvium and terrace deposits are of Pleistocene and late Tertiary (?) age, but most of the area is occupied by more strongly consolidated rocks of late Pennsylvanian and early Permian age. On this and following pages, where the rock succession in Elk County is described, statements of thickness and distribution apply to this county only unless otherwise indicated. Exposures of most of the outcropping Paleozoic rocks in the county are represented graphically in Figure 2 (middle Wolfcampian), Figure 3 (lower Wolfcampian), Figure 4 (upper Virgilian), Figure 5 (middle Virgilian), and Figure 6 (lower Virgilian).
Stream Valley Alluvium
Stream-laid deposits of gravel, sand, silt, and clay as much as 40 feet thick occupy the valleys of Elk and Fall Rivers. Thinner accumulations partly fill the valleys of smaller streams. In the larger valleys coarse material, predominantly chert, limestone, and sandstone gravel, commonly is found in a lower zone ranging from a fraction of an inch to 8 feet in thickness. Sand is intermingled with the pebbles, some of which are 2 to 3 inches in diameter. The upper part of the deposit consists mostly of clay and silt but grades downward into more sandy material. Colors generally are darker near the present land surface, but variations of tan and buff predominate in the lower parts.
The position of present stream valley alluvium, except very narrow belts in small valleys, and the position of the lowest recognizable terrace are shown together on Plate 1.
The thicker deposits of alluvium constitute the most important freshwater-bearing formation in Elk County.
Stream-laid deposits of clay, silt, sand, and gravel, of Pleistocene age, occur in terraces at elevations lower than those of material believed to have been deposited by streams in Late Tertiary time. Three terraces are recognized along parts of Elk River valley near Longton. The lowest one is narrow and discontinuous. In lithology and thickness the material of this terrace is similar to the alluvium below the present floodplain, and its position in reference to the river valley suggests correlation with, the Wiggam terrace along Cottonwood and Neosho Rivers farther north in Kansas (O'Connor, 1953, p. 6).
The most prominent and extensive Pleistocene terrace lies a few feet above the lowest terrace and about 15 to 20 feet above the present flood-plain. The material of this terrace is similar to that of the lower and younger valley fills. The position of this intermediate terrace suggests correlation with the Emporia terrace in Chase and Lyon counties (Moore and others, 1951, p. 6; O'Connor, 1953, p. 7). The Emporia terrace is judged to be late Kansan in age.
The third and highest Pleistocene terrace is recognized only in the vicinity of Longton, where it is 20 to 25 feet above the intermediate level. Material below this terrace consists of a thin zone of fine material underlain chiefly by chert gravel. Material in the two lower terraces yields considerable water to wells. The uppermost terrace, however, generally is above the water table.
Pliocene (?) Series
Remnants of a terrace ranging from about 100 to 150 feet above the river valley occur in isolated locations in the Fall River watershed. The deposits constituting the terrace are composed mainly of coarse chert gravels and are, probably at least in part, of late Tertiary age. The average thickness is a few feet. In a few places these chert gravels yield a small amount of water to shallow wells.
Kansas Geological Survey, Geology
Web version July 2002. Original publication date July 1958.
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