The Geography of Oklahoma encompasses terrain and ecosystems ranging from arid plains to subtropical forests and mountains.Oklahoma contains 10 distinctecological regions, more per square mile than in any other state by a wide margin.^[1] It is situated in theGreat Plains andU.S. Interior Highlands region near the geographical center of the 48contiguous states. Usually considered part of theSouth Central United States, Oklahoma is bounded on the east byArkansas andMissouri, on the north byKansas, on the northwest byColorado, on the far west byNew Mexico, and on the south and near-west byTexas.

The state has four primary mountain ranges: theArbuckle Mountains, theWichita Mountains, theOzark Mountains and theOuachita Mountains.^[2] Part of the U.S. Interior Highlands region, the Ozarks and Ouachitas form one of the only major highland regions between theRocky Mountains and theAppalachians.^[3]

A portion of theFlint 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.^[4] 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 reservoirs in the nation.^[4] Oklahoma covers an area of 69,898 square miles (181,030 km²), with 68,667 square miles (177,850 km²) of land and 1,231 square miles (3,190 km²) of water, making it the 20th-largest state in the United States.^[5] Generally, it is divided into seven geographical regions:Green Country (Northeast Oklahoma),Choctaw Country (Southeast Oklahoma),Central Oklahoma (Frontier Country),South Central Oklahoma (Chickasaw Country),Southwest Oklahoma (Great Plains Country),Northwest Oklahoma (Red Carpet Country), and theOklahoma Panhandle.

Situated between theGreat Plains and theOzark Plateau in theGulf of Mexico watershed,^[6] Oklahoma tends to slope gradually downward from its western to eastern boundaries.^[2][7] Its highest and lowest points follow this trend, with its highest peak,Black Mesa, at 4,368 feet (1,516 m) above sea level, situated near the far northwest corner of theOklahoma Panhandle. The state's lowest point is on theLittle River near its far southeastern boundary, which dips to 289 feet (88 m) above sea level.^[8]

Most of the state lies in two primarydrainage basins belonging to theRed andArkansas rivers, though the Lee and Little rivers also contain significant drainage basins.^[9] In the state'snorthwestern corner,semi-aridhigh plains harbor few natural forests and rolling to flat landscape with intermittentcanyons andmesa ranges like theGlass Mountains. Partial plains interrupted by small mountain ranges like theAntelope Hills and theWichita Mountains dotsouthwestern Oklahoma, and transitional prairie and woodlands cover thecentral portion of the state. The Ozark and Ouachita (pronounced Oh-Wa-Sheet-ah) Mountains rise from west to east over the state's eastern third, gradually increasing in elevation in an eastward direction.^[7][9]

Oklahoma had few natural lakes. Those that did exist were eitheroxbow orplaya lakes. Oklahoma has sixty-two oxbow lakes above 10 acres (0.040 km²) in size. The largest, near the Red River inMcCurtain County is 272 acres (1.10 km²). The prolonged drought that started in 1930 and created the condition called the "Dust Bowl", led to the construction of a great many reservoirs throughout the state. Now, Oklahoma has the largest number oflakes created by dams of any state in theUnited States, with more than 200.^[4]

Forests cover 24 percent of Oklahoma,^[4] andprairie grasslands, composed of shortgrass, mixed-grass, andtallgrass 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 andshrublands are the most prominent ecosystems, thoughpinyon pines,junipers, andponderosa pines grow near rivers and creek beds in the far western reaches of the panhandle.^[10]Marshlands,cypress forests and mixtures ofshortleaf pine,loblolly pine,sabal minor, and deciduous forests dominate the state'ssoutheastern quarter, while mixtures of largelypost oak,elm,cedar andpine forests cover the Ozark Mountains innortheastern Oklahoma. Many rare, relic species such assugar maple,bigtooth maple,southern live oak, andnolina inhabitSouthwestern Oklahoma and theWichita Mountains.^[9][10][11]

The state holds large populations ofwhite-tailed deer,coyotes,bobcats,elk, and birds such asquail,doves,cardinals,bald eagles,red-tailed hawks, andpheasants. In prairie ecosystems,american bison,greater prairie-chickens,badgers, andarmadillo are common, and some of the nation's largestprairie dog towns inhabit shortgrass prairie in the state's panhandle. TheCross Timbers, a region transitioning from prairie to woodlands in Central Oklahoma, harbors 351vertebrate species. The Ouachita Mountains are home toblack bear,red fox,grey fox, andriver otter populations, which coexist with a total of 328 vertebrate species in southeastern Oklahoma.^[10]

Oklahoma has 41state parks, twonational protected forests orgrasslands,^[12] 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,^[11] including the western portions of theOuachita National Forest, the largest and oldest national forest in the southern United States.^[13] With 39,000 acres (160 km²), theTallgrass Prairie Preserve in north-central Oklahoma is the largest protected area oftallgrass prairie in the world and is part of anecosystem that encompasses only 10 percent of its former land area, once covering 14 states.^[14] In addition, theBlack Kettle National Grassland covers 31,300 acres (127 km²) of prairie in southwestern Oklahoma.^[15] TheWichita Mountains Wildlife Refuge is the oldest and largest of ninenational wildlife refuges in the state^[16] and was founded in 1901, encompassing 59,020 acres (238.8 km²).^[17] Of Oklahoma's federally protected park or recreational sites, theChickasaw National Recreation Area is the largest, with 4,500 acres (18 km²).^[18] Other federal protected sites include theSanta Fe andTrail of Tears national historic trails, theFort Smith andWashita Battlefield national historic sites, and theOklahoma City National Memorial.^[19]

Oklahoma sits at a frequent crossroads between three different air masses: warm, humid air from the Gulf of Mexico; warm to hot, dry air from Mexico and the Southwestern U.S.; and cold, dry air from Canada. Especially from fall to spring, Oklahoma sees frequent air mass changes, which can produce drastic swings in both temperature and humidity. Much of the state is often subjected to extremes in temperature, wind, drought, and rainfall.^[20] Most of the state lies in an area known asTornado Alley characterized by frequent interaction between cold and warm air masses, producingsevere weather, with the highest-risk months from April to June.^[8] An average of 62tornadoes strike the state per year, making that one of the highest rates in the world.^[21] Due to its position between zones of differing prevailing temperature and winds, weather patterns within the state can vary widely between relatively short distances.^[8] Precipitation occurs year-round, but average monthly precipitation is generally lowest in the winter months, rising dramatically to a peak in May (the year's wettest month virtually statewide, owing to frequent, and not uncommonly severe, thunderstorm activity), and decreases again by mid-summer, when long stretches of hot, dry weather are common in July and August many years. Early to mid-fall (September and October) often sees a secondary precipitation maximum. From late October to December, precipitation generally decreases again.

Eastern Oklahoma has a temperatehumid subtropical climate (KöppenCfa) heavily influenced by southerly winds bringing moisture from theGulf of Mexico and has hot, humid summers and generally cold winters, but with cold spells, accompanied by snow, sleet or freezing rain. This transitions progressively to asemi-arid zone (KöppenBSk) in thehigh plains of the Panhandle, where a drier climate prevails, with somewhat-colder winters and similarly-hot summers but much lower humidity. Other central to western areas of the state, includingLawton andEnid in the transition zone, are also less affected by moisture from the Gulf of Mexico. They also tend to be drier than Oklahoma's eastern counties.^[20] 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 over 40 and as high as 56 inches (1,420 mm), while areas of the panhandle average 58 °F (14 °C), with an annual rainfall under 17 inches (430 mm).^[8] All of the state frequently experiences temperatures above 100 °F (38 °C), or below 0 °F (−18 °C) (though subzero temperatures are rare in southeastern Oklahoma),^[20] and snowfall ranges from an average of less than 4 inches (10 cm) in the far south to just over 20 inches (51 cm) on the border ofColorado in the panhandle.^[8] The state is home to theNational Storm Prediction Center of theNational Weather Service located inNorman.^[22] Winter and spring weather often are influenced by theEl Niño Southern Oscillation. Winters during El Niño are cooler than average and wetter across the western portion of the state due to an amplified southern jet stream. During La Niña, the storm track is further north, therefore winters are warmer than average and drier in the western part of the state.

• 2009–19 Oklahoma earthquake swarms
• Geology of Oklahoma
• List of Oklahoma tri-points
• Zodletone Mountain

• Robert Lowitt, "Environment and cultural ecology",Encyclopedia of Oklahoma History and Culture

• Geography of Oklahoma

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