This article: Oklahoma is the 20th-largest state in the United States, covering an area of 69,899 square miles (181,040 km2), with 68,595 square miles (177,660 km2) of land and 1,304 square miles (3,380 km2) of water. It 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. Much of its border with Texas lies along the Southern Oklahoma Aulacogen, a failed continental rift. The geologic figure defines the placement of the Red River.
The Oklahoma panhandle's Western edge is out of alignment with its Texas border. The Oklahoma/New Mexico border is 2.1 miles (3.4 km) to 2.2 miles (3.5 km) east of the Texas line. The border between Texas and New Mexico was set first as a result of a survey by Spain in 1819. It was then set along the 103rd meridian. In the 1890s, when Oklahoma was formally surveyed using more accurate surveying equipment and techniques, it was discovered the Texas line was not set along the 103rd meridian. Surveying techniques were not as accurate in 1819, and the actual 103rd meridian was approximately 2.2 miles (3.5 km) to the east. It was much easier to leave the mistake than for Texas to cede land to New Mexico to correct the surveying error. The placement of the Oklahoma/New Mexico border represents the true 103rd meridian.
Cimarron County in Oklahoma's panhandle is the only county in the United States that touches four other states: New Mexico, Texas, Colorado, and Kansas. contains an answer for the question: What two states have their border along the Southern Oklahoma Aulacogen?, what is it ?


Texas