Crustal stretching beginning about 15 million years ago created Basin and Range topography in central and southern Arizona, caused volcanic activity near Jerome, and induced movement along the Verde Fault. This movement exposed the tip of the United Verde ore body at one place on Cleopatra Hill and moved the UVX ore body to below the surface. Basalt, laid down between 15 and 10 million years ago, covers the surface beneath the UVX headframes and Jerome State Historic Park. The basalt, the top layer of the Hickey Formation, caps layers of sedimentary rock. The natural rock features in and around Jerome were greatly altered by mining. The town is underlain by of mine shafts. These may have contributed to the subsidence that destroyed some of Jerome's buildings, which slid slowly downhill during the first half of the 20th century. The United Verde open pit, about deep, is on the edge of town next to Cleopatra Hill. The side of the pit consists of Precambrian gabbro. Mine shafts beneath the pit extend to below the surface. The Hohokam were the first people known to have lived and farmed near Jerome from 700 to 1125 BCE. Later, long before the arrival of Europeans, it is likely that other native peoples mined the United Verde ore body for the colorful copper-bearing minerals malachite and azurite. The top of the ore body was accessible because it was visible on the surface. The first Europeans to arrive in the area were the Spanish conquistadors. At the time the area was part of "New Mexico", and the Spaniards often organized silver and gold prospecting expeditions in the area. In 1585, Spanish explorers made note of the ore but did not mine it because their government had sent them to find gold and silver, not copper. The area became part of Mexico when Mexico gained its independence from Spain in 1821, and part of the United States by terms of the 1848 Treaty of Guadalupe Hidalgo, which concluded the Mexican–American War. The war's major consequence was the Mexican Cession of the northern territories of Alta California and Santa Fe de Nuevo México to the United States. Angus McKinnon and Morris A. Ruffner filed the first copper mining claims at this location in 1876. In 1880, Frederick A. Tritle, the governor of the Arizona Territory, and Frederick F. Thomas, a mining engineer from San Francisco, bought these claims from the original owners.