Colorado is one of the states with the highest altitude in the mid-western United States. It is divided into four main regions: the Great Plains in the east, the Rocky Mountains in the center, the Colorado Plain in the west, and the Intermontane Basin in the northwest. The summers are cool and dry, and the winters are cold and snowy. The average temperature is 15 ° C in summer and -6 ° C in winter. The United States Air Force is located in Colorado Springs. Denver, capital of Colorado, has an area of 269,619 km² and a population (year 2000) of 4,301,260 people. Cheeseburger originated in Denver. The world's first rodeo was held in 1869 on Deer Trail. Tim Allen (actor), M. Scott Carpenter (astronaut) and Gene Fowler (writer) are among the celebrities of the State of Colorado. In addition, the founders of the South Park series and the Rock-Pop music group called OneRepublic came from here.