Situated in the southwest corner of Arizona on the Colorado River, historic Yuma got its start as a river crossing and a U.S. Army fort. Today the city is the location of the Marine Corps Air Station Yuma and the Yuma Proving Grounds, an installation that tests new Army equipment. Agribusiness and the trucking industry are also major employers. Many natural desert areas are within a few hour's drive in both Arizona and California. The border with Mexico is nearby, with the Sea of Cortez about 60 miles to the south. According to the Census Bureau, more than 85,000 retirees make Yuma their winter residence.