Physical Geography

Oklahoma has generally flat to gently rolling land, with scattered highlands and low mountains in the southern and eastern portions of the state.

Oklahoma's Panhandle is within the Great Plains region of the western United States. It has the state's greatest overall elevation and its highest point, Black Mesa, which reaches 4,973 feet (1,516 m) above sea level. In general, elevations decrease eastward across the state.

Central Oklahoma is part of the Central Lowlands region of the United States. In the Oklahoma portion of this region, the terrain is generally rolling to level, except in the Wichita Mountains in the southwest and the Arbuckle Mountains in the south-central part of the state.

Much of eastern Oklahoma is occupied by the scenic hills of the Ozark Plateau in the northeast and the Ouachita Mountains in the southeast. Eastern Oklahoma's highest point, about 3,000 feet (900 m), is in the Ouachitas. In the extreme southeastern part of the state is a small portion of the Gulf Coastal Plain region of the United States.

The lowest point in the state—287 feet (87 m) above sea level—is here.

Oklahoma has no major natural lakes, but has several rivers of considerable length. The major lakes are man-made reservoirs impounded by dams on these rivers, the largest reservoirs being Eufaula, Texoma, Lake o' the Cherokees, Robert S. Kerr, Oologah, and Keystone.

All of Oklahoma is in the drainage basin of the Mississippi River. Both of the major rivers—the Red and the Arkansas—enter the Mississippi. The chief tributaries of the Arkansas are the Canadian, the North Canadian, and the Cimarron. Those of the Red River are the North Fork and the Washita. The rivers in the west are long, but wide, shallow, and slow-moving. They are subject to destructive flash floods in spring and summer, and often run dry in the dry season. In the east the rivers are generally shorter, but swifter and deeper.

In general, Oklahoma has a continental climate, with warm, humid summers and cool, dry winters. However, tropical influences from the Gulf of Mexico make southeastern Oklahoma warmer and wetter than the rest of the state. Temperatures and precipitation decrease from southeast to northwest across the state. January temperatures average about 43° F. (6° C.) in the southeast and about 35° F. (2° C.) in the Panhandle. July temperatures for the same areas average 83° F. (28° C.) and 81° F. (27° C.), respectively. Precipitation, mostly rain, is about 50 inches (1,270 mm) in the southeast, while in the Panhandle it averages about 15 inches (380 mm).

In the western plains area rainfall is light and any increase or decrease can cause disasters such as flash floods or prolonged droughts. The worst of these was the long drought of the 1930's that turned western Oklahoma into a “dust bowl.” The state is also subject to tornadoes.

Grasses are the native vegetation of most of Oklahoma. The Panhandle supports short grasses and shrubs, such as buffalo grass and sagebrush. From the Panhandle eastward to about the center of the state, tall-grass prairies once predominated but have been replaced largely by farmland. A landscape of grassy tracts interspersed with areas of shrubs and woods prevails in most of the rest of Oklahoma.

The southeastern portion of the state sup ports markedly different plant life. Found here are hardwood and pine forests. Red and white oak, hickory, and loblolly and short-leaf pine are the primary trees. Pines are especially prevalent in the Ouachitas.