The area consists of a gently rolling to hilly, dissected limestone plateau and of the low, rugged Arbuckle Mountains. Stream valleys are shallow and narrow in their upper reaches but deepen and broaden near the eastern edge of the area. Steep slopes border the valleys of larger streams and are along the side slopes of flat-topped plateaus and in most of the Arbuckle Mountains. Relief is mainly several meters, but the large valleys are about 50 m below the adjacent uplands. Average annual precipitation - 700 to 1,025 mm.
Maximum precipitation is in spring and in fall.
More than half of the precipitation falls during the frost-free period. The moderate but somewhat erratic rainfall is the source of water for crops, pasture, and range. The large rivers flow all year. Several large lakes and flood-detention reservoirs are potential sources of water for irrigation but are little used for this purpose now. Deep ground water is abundant, and many springs and wells are throughout the area.