The Buffalo River has cut deeply onto the bedrock, leaving tall, vertical bluffs standing at river bends. In some areas the river is confined by bedrock; in others it meanders through alluvial bottoms. The channel is vertically stable as the bedrock is either exposed or covered with a thin layer of gravel and sand. The river is characterized by quiet pools separated by short riffles. From Ponca to Pruitt the river falls an average of 13 feet per mile. From Pruitt to Highway 65 the average gradient is five feet per mile, and from there to the mouth it is about three feet per mile. The elevations within the Buffalo River watershed range from 2,576 feet above sea level in the Boston mountains to 351 feet above sea level where the Buffalo River empties into the White River. The hills or ridge tops surrounding the river are usually narrow and winding, the sides alternate in steep slopes and vertical escarpments. The watershed is characterized by three physiographic regions, the Springfield Plateau, the Boston Mountains, and the Salem Plateau. The Springfield Plateau occupies about 47% of the Buffalo's watershed and is underlain by limestone and cherty limestone of Mississippian age. Land surface altitudes range from 1,000 to 1,700 ft but locally topographic relief rarely exceeds 200 to 300 ft. Sinkholes and springs are common in this region. The Boston Mountains occupies 34% of the watershed. They are underlain by sandstone, shale, and limestone of late Mississippian to Pennsylvanian age. Land surface altitude ranges from 1,200 to more than 2,300 ft above sea level and topographic relief is as much as 1,000 ft in some places. The topography is rugged with narrow divides separating steep-sided valleys. Finally, the Salem Plateau occupies 19% and is underlain by rocks of the Cambrian and Ordovician age. The upland is characterized by gently rolling hills and local relief is 50 to 100 ft in the upland area.