HA 2 (1)ogs.ou.edu/docs/hydrologicatlases/HA2P1.pdfvalleys separated by narrow flat-topped ridges....
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HA 2 (1)ogs.ou.edu/docs/hydrologicatlases/HA2P1.pdfvalleys separated by narrow flat-topped ridges. Downcutting by Spring and Spavinaw Creeks and the Illinois River has exposed rocks