Oklahoma occupies a transitional zone between the drier Great Plains to the west and the humid, forested U.S. Interior Highlands to the east. This geographic diversity makes it one of the most ecologically diverse states in the nation for its size. The state is bounded by six others: Texas to the south and west, New Mexico to the far west (the Panhandle), Colorado and Kansas to the north, and Missouri and Arkansas to the east.
The terrain shifts dramatically from the flat, high-elevation shortgrass prairies of the western panhandle to the rolling, tree-covered hills and ancient mountains of the east. The state is drained by two massive river basins: the Red River, which forms the southern border with Texas, and the Arkansas River, which flows through the state's northeastern quadrant.
Due to extensive damming projects initiated to control flooding and generate power after the 1930s, Oklahoma boasts over 200 human-made lakes—the highest number of any state. Natural resources are abundant, including massive subterranean aquifers (like the Ogallala), rich agricultural soils in the central plains, and vast deposits of petroleum, natural gas, and iodine.