Although the popular image of the state is one of unending flatlands, Kansas has a diverse topography. Three main land regions define the state. The eastern third consists of the Osage Plains, Flint Hills, Dissected Till Plains, and Arkansas River Lowlands. The central third comprises the Smoky Hills (which include the Dakota sandstone formations, Greenhorn limestone formations, and chalk deposits) to the north and several lowland regions to the south. To the west are the Great Plains proper, divided into the Dissected High Plains and the High Plains. Kansas generally slopes eastward from a maximum elevation of 4,039 ft (1,232 m) at Mt. Sunflower (a mountain in name only) on the Colorado border to 679 ft (207 m) by the Verdigris River at the Oklahoma border. More than 50,000 streams run through the state, and there are hundreds of artificial lakes. Major rivers include the Missouri, which defines the state's northeastern boundary; the Arkansas, which runs through Wichita; and the Kansas (Kaw), which runs through Topeka and joins the Missouri at Kansas City.
The geographic center of the 48 contiguous states is located in Smith County, in north-central Kansas, at 39°50'N and 98°35'W. Forty miles (64 km) south of this point, in Osborne County at 39°13'27"N and 98°32'31"W, is the North American geodetic datum, the controlling point for all land surveys in the US, Canada, and Mexico. Extensive beds of prehistoric ocean fossils lie in the chalk beds of two western counties, Logan and Gove.