|Oklahoma is the 20th largest state of the US by size and the 28th largest by population. It has a total area of 69,898 square miles including 1,231 square miles of area under water. In 2008, the population was approximately 3.6 million with a population density of 52.7 per square mile. It is bounded on the north by Kansas, on the east by Arkansas and Missouri, on the northwest by Colorado, on the south and near-west by Texas and on the far west by New Mexico. Located in the South Central region of the country, the state lies between the Great Plains and the Ozark Plateau. Black Mesa is its highest point with a height of 4,973 feet whereas the lowest point is on the Little River with a depth of 289 feet. It was admitted to the Union in 1907 as 46th state of the USA. Oklahoma is a leading producer of oil and natural gas, and its economy is based on agriculture, aviation, telecommunications, energy and biotechnology. More than 60 percent of population is concentrated in the metropolitan areas of Oklahoma City and Tulsa, the prime centers of the state's economical activities. Oklahoma City is also the capital of the state.