The geography of Texas spans a wide range of features and timelines. Texas is the southernmost part of the Great Plains, which ends in the south against the folded Sierra Madre Oriental of Mexico. It is in the south-central part of the United States of America. It is considered to form part of the Southern United StatesU.S. South and also part of the Southwestern United StatesU.S. Southwest. The Rio Grande, Red River (Mississippi watershed)Red River and Sabine River (Texas-Louisiana)Sabine River all provide natural state lines where Texas borders Oklahoma on the north, Louisiana and Arkansas on the east, and New Mexico and the MexicoMexican states of Chihuahua (state)Chihuahua, Coahuila, Nuevo León, and Tamaulipas to the south. By residents, the state is generally divided into North Texas, East Texas, Central Texas, South Texas, and West Texas, but according to the Texas Almanac, Texas has four major physical regions: Geography of Texas#The Gulf Coastal PlainsGulf Coastal Plains, Geography of Texas#The Interior LowlandsInterior Lowlands, Geography of Texas#The Great PlainsGreat Plains, and Geography of Texas#The Basin and Range ProvinceThe Basin and Range Province. This is the difference between human geography and physical geography. Some regions of Texas are associated with the South more than the Southwest (primarily East Texas and North Texas), while other regions share more similarities with the Southwest than the South (primarily West Texas and South Texas). The Texas Panhandle and South Plains regions don't fit either category; they seem to have more in common with parts of the Midwestern United States. The size of Texas prohibits easy categorization of the entire state wholly in any recognized region of the United States; geographic, economic, and even cultural diversity between regions of the state preclude treating Texas as a region in its own right. Source: http://en.wikipedia.org/wiki/Texas