Post Rock Country lies in the heart of the Smoky Hills, named for the early-morning fog that forms in its valleys. The region is defined by rock outcroppings formed more than 66 million years ago during the Cretaceous Age, when the ancient inland sea that covered much of Kansas was deeper and larger than in earlier eras. Two distinct types of outcroppings occur along the Byway: Greenhorn Limestone and Dakota Formation Sandstone. Found in the center of the Smoky Hills, Greenhorn or post rock limestone was deposited in a shallower part of the Cretaceous sea, and near the top of the Greenhorn layer a bed called Fencepost limestone, often exposed by erosion, became especially important to early settlers. Because timber was scarce, they used this foot-thick limestone layer, marked by a distinctive reddish band, in place of wood to build fenceposts, homes, churches, businesses, bridges, and sidewalks. Dakota Formation Sandstone occurs in a belt from Rice County in the south to Washington County in the north; these sandstones are the remains of beach sands and sediments deposited by rivers draining into the early Cretaceous sea, and they often cap the hills and buttes in this part of the Smoky Hills. The Pawnee Nation often created petroglyphs on the sandstone, some of which can be seen at Wilson Lake. Here, the Smoky Hills support mixed prairie, marking a transition from the eastern tallgrass prairies to the western shortgrass prairie. Trees grew along river and stream valleys but were uncommon on the highland, and the lack of tree cover, soil composition, and prevalence of limestone created a rugged geography that produced many small farming towns, each with a distinctive history and culture, including Lucas, Wilson, and Sylvan Grove.