Oklahoma is the 20th-largest state in the United States, covering an area of 69,898 square miles (181,035 km²), with 68,667 square miles (177847 km²) of land and 1,231 square miles (3,188 km²) of water. It is one of six states on the Frontier Strip, and lies partly in the Great Plains near the geographical center of the 48 contiguous states. It is bounded on the east by Arkansas and Missouri, on the north by Kansas, on the northwest by Colorado, on the far west by New Mexico, and on the south and near-west by Texas.

Topography

Oklahoma is situated between the Great Plains and the Ozark Plateau in the Gulf of Mexico watershed, generally sloping from the high plains of its western boundary to the low wetlands of its southeastern boundary. Its highest and lowest points follow this trend, with its highest peak, Black Mesa, at 4,973 feet (1,516 m) above sea level, situated near its far northwest corner in the Oklahoma Panhandle. The state's lowest point is on the Little River near its far southeastern boundary, which dips to 289 feet (88 m) above sea level.

The state has four primary mountain ranges: the Ouachita Mountains, the Arbuckle Mountains, the Wichita Mountains, and the Ozark Mountains. The U.S. Interior Highlands Region, which contains the Ozark and Ouachita Mountains, is the only major mountainous region between the Rocky Mountains and the Appalachians. A portion of the Flint Hills stretches into north-central Oklahoma, and in the state's southeastern corner, Cavanal Hill is officially regarded as the world's tallest hill; at 1,999 feet (609 m), it fails the definition of a mountain by one foot. More than 500 named creeks and rivers make up Oklahoma's waterways, and with 200 lakes created by dams, it holds the highest number of artificial reservoirs in the nation.

Among the most ecologically diverse states, Oklahoma is one of four to harbor more than 10 distinct ecological regions, containing eleven within its borders, more per square mile than in any other state. Marked by differences in geographical diversity between its western and eastern halves, eastern Oklahoma touches eight ecological regions, while its western half holds three.

Most of the state lies in two primary drainage basins belonging to the Red and Arkansas rivers, though the Lee and Little rivers also contain significant drainage basins. In the state’s northwestern corner, semi-arid high plains harbor few natural forests and rolling to flat landscape with intermittent canyons and mesa ranges like the Glass Mountains. Partial plains interrupted by small mountain ranges like the Antelope Hills and the Wichita Mountains dot southwestern Oklahoma, and transitional prairie and woodlands cover the central portion of the state. The Ozark and Ouachita Mountains rise from west to east over the state's eastern third, gradually increasing in elevation in an eastward direction.

Flora and fauna

Forests cover 24 percent of Oklahoma, and prairie grasslands, composed of shortgrass, mixed-grass, and tallgrass prairie, harbor expansive ecosystems in the state's central and western portions. Where rainfall is sparse in the western regions of the state, shortgrass prairie and shrublands are the most prominent ecosystems, though pinyon pines, junipers, and ponderosa pines grow near rivers and creek beds in the far western reaches of the panhandle. Marshlands, cypress forests and mixtures of shortleaf pine, loblolly pine and deciduous forests dominate the state's southeastern quarter, while mixtures of largely post oak, elm, cedar and pine forests cover the Ozark Mountains in northeastern Oklahoma.

The state holds large populations of white-tailed deer, coyotes, bobcats, elk, and migrating birds such as quail, doves, cardinals, bald eagles, red-tailed hawks, and pheasants. In prairie ecosystems, american bison, greater prairie-chickens, badgers, and armadillo are common, and some of the nation's largest prairie dog towns inhabit shortgrass prairie in the state's panhandle. The Cross Timbers, a region transitioning from prairie to woodlands in Central Oklahoma, harbors 351 vertebrate species. The Ouachita Mountains are home to black bear, red fox, grey fox, and river otter populations, which coexist with a total of 328 vertebrate species in southeastern Oklahoma.

Protected lands

Oklahoma has 50 state parks, six national parks or protected regions, two national protected forests or grasslands, and a network of wildlife preserves and conservation areas. Six percent of the state's 10 million acres (40,000 km²) of forest is public land, including the western portions of the Ouachita National Forest, the largest and oldest national forest in the southern United States. With 39,000 acres (158 km²), the Tallgrass Prairie Preserve in north-central Oklahoma is the largest protected area of tallgrass prairie in the world and is part of an ecosystem that encompasses only 10 percent of its former land area, once covering 14 states. In addition, the Black Kettle National Grassland covers 31,300 acres (127 km²) of prairie in southwestern Oklahoma. The Wichita Mountains Wildlife Refuge is the oldest and largest of nine national wildlife refuges in the state and was founded in 1901, encompassing 59,020 acres (238.8 km²). Of Oklahoma's federally protected park or recreational sites, the Chickasaw National Recreation Area is the largest, with 4,500 acres (18 km²). Other federal protected sites include the Santa Fe and Trail of Tears national historic trails, the Fort Smith and Washita Battlefield national historic sites, and the Oklahoma City National Memorial.

Climate

Oklahoma is located in a temperate region and experiences occasional extremes of temperature and precipitation typical in a continental climate. Most of the state lies in an area known as Tornado Alley characterized by frequent interaction between cold and warm air masses producing severe weather. An average 54 tornadoes strike the state per year—one of the highest rates in the world. Because of its position between zones of differing prevailing temperature and winds, weather patterns within the state can vary widely between relatively short distances. A humid subtropical zone along the state's southeastern border is influenced heavily by southerly winds bringing moisture from the Gulf of Mexico, but transitions progressively to a semi-arid zone in the high plains of the panhandle rarely touched by southern moisture. Precipitation and temperatures fall from east to west accordingly, with areas in the southeast averaging an annual temperature of 62 °F (17 °C) and an annual rainfall of 56 inches (1,420 mm), while areas of the panhandle average 58 °F (14 °C), with an annual rainfall under 17 inches (430 mm). All of the state frequently experiences temperatures above 100 °F (38 °C) or below 0 °F (−18 °C), and snowfall ranges from an average of less than 4 inches (10 cm) in the south to just over 20 inches (51 cm) on the border of Colorado in the panhandle. The state is home to the National Storm Prediction Center of the National Weather Service located at Norman.