The sedimentary rocks contain numerous dikes and sills of diabase and basalt. Other local areas are underlain by limestone. Topography is mostly gently sloping or sloping. Steeper slopes are mostly on the ridges at higher elevations or on side slopes adjacent to drainageways. Average annual precipitation -900 to 1,150 mm.
Maximum precipitation is in spring and early in summer.
Droughts of 10 to 14 days are common in summer. Springs are common in rural areas and provide water for many farmsteads. Water for irrigation comes from streams, ponds, and wells. Shallow wells are important in rural areas, but most of the wells supply a limited quantity of water. Water for urban areas is supplied largely by municipal reservoirs.