The rocks that crop out in Lyon County are of sedimentary origin; their areal extent is shown on Plate 1. The rocks exposed at the surface range in age from Pennsylvanian to Recent. In pages devoted to descriptions of the rock succession of Lyon County, statements of thickness and distribution apply to this county only, unless otherwise indicated.
Recent and Wisconsinan Stages
Deposits of stream-laid gravel, sand, silt, and clay, together with occasional cobbles and boulders, occur in the principal stream valleys and constitute the floodplains of the valley. The maximum accumulations are 40 to 50 feet thick. Deposits in the smaller valleys are thinner and more variable in lithology.
The coarse fraction of the alluvium of Cottonwood River valley contains considerable amounts of well-rounded quartz sand derived from Cretaceous sandstones in the headwaters area of the river. Marais des Cygnes and Verdigris rivers and Neosho River above its junction with Cottonwood River contain only small amounts of rounded quartz sand in the coarse fraction of the alluvial deposits, derived entirely from rocks of Permian and Pennsylvanian age which they drain.
All the larger streams contain large amounts of coarse chert gravel in the basal part of the alluvium and commonly considerable amounts of sand-size chert grains. Limestone and shale detritus, mollusk shells, and locally woody plant material occur with the quartz and chert sand and gravel. The finer material, which occurs chiefly in the upper and middle parts of the deposits, consists of silt and clay generally sandy in the lower part and nearly free of sand in the upper part (Pl. 4A and B). The lower part of the silt-clay section generally is calcareous. Descriptions of the alluvium are given in the record of test holes at the end of this report and are shown in cross sections in Figure 3. These deposits constitute the alluvial floodplain and are subject to frequent flooding.
The extent of stream-valley alluvium, except very narrow belts in small valleys, is shown on Plate 1. It is one of the most important sources of ground water. In the small tributary valleys, older Pleistocene terrace deposits are included with the alluvium.
Of the several widespread loesses in Kansas, only the Peoria loess is present in amounts sufficient to be recognized, and it forms only a thin and discontinuous mantle on the upland flats and some of the terraces along the major stream valleys. It ranges in thickness from a featheredge to about 5 feet locally. Because of their thinness, irregular and patchy distribution, and unimportance as a source of ground water, loess deposits were not mapped.
Illinoian Stage (?)
Two Pleistocene terraces can be recognized and mapped above the valley alluvium.
Wiggam terrace--The youngest of these terraces has a surface and basal elevation 5 to 20 feet higher than corresponding parts of the alluvium. The sediments comprising these deposits are similar to those of the alluvium and have a maximum thickness of about 45 feet (Fig. 3, and record of test hole logs at end of report).
For the purposes of this report this terrace is named the Wiggam terrace for Wiggam Station on the Atchison, Topeka, and Santa Fe Railway east of Emporia (NE NW sec. 21, T. 19 S., R. 12 E.). It is a well-defined and extensive terrace along Cottonwood and Neosho rivers. Cross section D-D' (Fig. 3), just west of Wiggam Station, illustrates the relation between Cottonwood and Neosho River alluvium and this terrace. It is probably represented along the Verdigris and Marais des Cygnes rivers but was not differentiated on Plate 1. This terrace is not subject to flooding by Neosho or Cottonwood River.
The age of these terrace deposits is not certain. Although probably Illinoian in age they may be younger, as the relation of the thin discontinuous mantle of Peoria loess in the area to the terrace is not clear. It is an important source of ground water.
Emporia terrace--The City of Emporia is built largely on an extensive terrace above the Wiggam terrace (Pl. 1; Fig. 3). This terrace has been named the Emporia terrace (Moore, Jewett, and O'Connor, 1951, p. 6). Basal deposits of this terrace rest on an eroded surface which ranges from about the level of the present alluvial floodplain surface to approximately 20 feet above the floodplain surface. It consists of sand and gravel in the basal 3 to 20 feet, silt, volcanic ash, caliche nodules, and clay in the remaining upper part. Maximum thickness of these deposits is about 50 feet. Except for local deposits of Pearlette volcanic ash which occur within this terrace, it is similar in lithology to material in the alluvium and Wiggam terrace. Most of the deposit, where thick, is calcareous.
Plate 4D shows a gravel pit in the basal part of the Emporia terrace on the Bechtold farm (NW NW sec. 9, T. 19 S., R. 10 E.). From this and adjacent quarries, several teeth and other vertebrate skeletal remains were recovered in quarrying operations. According to W. D. Frankforter (personal communication), the fossil material from this quarry indicates a post-Kansan climax age for the gravels, equivalent to the Grand Island member of the Meade formation in other areas of Kansas.
A 3- to 4-foot lentil of Pearlette volcanic ash occurs locally in the silt and clay (Sappa) just above the basal sand and gravel of this terrace and was mined at one time within the City of Emporia (Frye, Swineford, and Leonard, 1948, pp. 508-510; Carey and others, 1951).
According to John C. Frye (personal communication), exposures of this terrace in new road cuts along U.S. 50-S (near Cen. sec. 10, T. 19 S., R. 10 E.) show a partial Sangamon soil developed on top of the Sappa member, overlain by about 3 or 4 feet of Peoria loess.
The various lines of evidence indicate a Kansan age for the Emporia terrace.
The extent of this terrace along Cottonwood and Neosho River valleys is shown on Plate 1. It is an important source of ground water and is not flooded by Cottonwood or Neosho River. Terrace deposits of Kansan age are probably represented along the Verdigris and Marais des Cygnes rivers also, but were not differentiated from Illinoian (?) terrace deposits on Plate 1.
Kansas Geological Survey, Lyon County Geohydrology
Web version Sept. 2001. Original publication date March 1953.
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