The ancestral Arkansas River flowed from the Wichita vicinity eastward across Butler and Greenwood counties into what is now the Fall River drainage basin (fig. 2). The exact position of the ancestral Arkansas is problematic. However, such a dispersal route is necessary to explain the presence of exotic pebbles in chert gravels in the headwaters of the Walnut River basin near the crest of the Flint Hills (fig. 11).
Fig. 11. Chert Gravel near Flint Hills Crest. High-terrace chert gravel resting on Kinney Limestone, in headwaters of the Little Walnut drainage, near crest of Flint Hills [elevation, 450 m (1,475 ft) or more] in eastern Butler County. This terrace gravel contains exotic quartzite derived from the west. The presence of exotics here implies a reversal in drainage since the Miocene. Scale pole marked in feet.
The ancestral Verdigris River flowed eastward across the central portion of the study region--Marion, Chase, Lyon, and Coffey counties (fig. 2). This through drainage is demonstrated by the belts of exotic-bearing gravels on the Verdigris-Cottonwood and Verdigris-Neosho drainage divides and across southern Coffey County, as well as by isolated exotic pebbles on hilltops of the Flint Hills.
The ancestral Neosho River came from the northeast, as evidenced by the broad belt of exotic-bearing gravel that slopes toward the southwest from the Missouri-Arkansas drainage divide in Anderson County (figs. 2, 12). Presumably, the ancestral Verdigris and Neosho rivers joined in the vicinity of southeastern Coffey or northwestern Allen counties, from whence the ancestral Neosho followed a path similar to, but west of, the modern Neosho River.
Fig. 12. Anderson County Gravel. Exposure of exotic-bearing chert gravel near the Missouri-Arkansas drainage divide in central Anderson County. The gravel is about 2 m (6 ft) thick in this section.
The ancestral Marais des Cygnes River originated in the Flint Hills region and flowed eastward across northern Lyon and southern Osage counties (fig. 2). This local drainage is suggested by hilltop gravels north of the Marais des Cygnes valley, which do not contain exotic pebbles derived from west of the Flint Hills. A northern branch of the ancestral Marais des Cygnes is indicated by exotic-bearing chert gravels on the Wakarusa-Marais des Cygnes divide in northern Osage County. These rivers may have connected with the ancestral Neosho somewhere to the east.
These ancestral drainages bear no relation to many of the modern rivers, in particular the Walnut, Cottonwood, and upper Neosho. The prominent northwest-trending valley orientation of modern rivers is also not evident in the ancestral drainage pattern.
Kansas Geological Survey
Web version March 18, 1998
http://www.kgs.ku.edu/Current/1997/aber/aber11.html
email:lbrosius@kgs.ku.edu