Pinal County was formed from portions of Maricopa and Pima counties on Feb. 1, 1875, in response to the petition of residents of the upper Gila River Valley, as "Act #1" of the Eighth Territorial Legislature. Florence, established in 1866, was designated and has remained the county seat. The county encompasses 5,371square miles, of which 30 are water. In both the economy and geography, Pinal County has two distinct regions. The eastern portion is characterized by mountains, elevations to 6,000 feet and copper mining. The western area is primarily low desert valleys and irrigated agriculture. The communities of Mammoth, Oracle, San Manuel, and Kearny are active in copper mining, smelting, milling and refining. Arizona City, Eloy, Maricopa, Picacho, Red Rock and Stanfield have agricultural based-economies. Apache Junction, Arizona City, Coolidge, Eloy, and particularly Casa Grande have diversified their economic base to include manufacturing, trade and services. This expansion and diversification has been facilitated by their location in the major growth corridor between Phoenix and Tucson near the junction of I-10 and I-8, except for Apache Junction, which is to the east of burgeoning Mesa. All of Pinal County is an Enterprise Zone. The county is home to many interesting attractions, including the Casa Grande Ruins National Monument, Picacho Peak State Park, Picacho Reservoir, Boyce Thompson Southwestern Arboretum, Oracle State Park and the Biosphere, McFarland State Park, Lost Dutchman State Park, Skydive Arizona, the world’s largest skydiving drop-zone, and the Florence Historical District, with 120 buildings on the National Register. The state of Arizona is the county’s largest landholder with 35.3 percent, followed by individuals and corporations, 25.7 percent; Indian reservations, 20.3 percent; the U.S. Forest Service and Bureau of Land Management, 17.5 percent, and the remaining 1.2 percent is other public land.