Casper is the second largest city in Wyoming and its leading industrial center. Surrounded by large oil fields, including the famous Teapot Dome and Salt Creek fields, it is a business center for oil companies. Oil refining is the chief industry. Mining and milling of uranium is also important, as well as shipping and wholesaling for the surrounding stock-raising and farm area. Casper is located 150 miles northwest of Cheyenne on the North Platte River, and is the seat of Natrona County. Fort Casper was built on this site in 1863 as a Pony Express depot and to protect travelers on the Oregon Trail. Casper was founded in 1888.