The long history of Cortez begins in 1862 when a group of Mexicans discovered silver ore next to Mount Tenabo. The ore was shipped to Austin, where it raised considerable interest among the locals. An eight-man prospecting party, led by Simeon Wenban, traveled to the district in March 1863 and found silver in the gulches southwest of Mount Tenabo. Wenban and his group located substantial silver ledges, which sustained Cortez for many years even though the isolated location of the deposits made development difficult. In 1864 Wenban formed a partnership with George Hearst, father of William Randolph Hearst, and that summer the first mill in the district was built. An 8-stamp mill, the Cortez, was constructed in nearby Mill Canyon, but its success was limited and most ore was still shipped to Austin.

By 1865, three mining companies were active in the district: the Cortez Company, the Edward Everett Silver Mining Company, and the Pizarro Silver Mining Company. The Cortez company spent $100,000 in 1865 to enlarge the Mill Canyon Mill to 16 stamps in response to the huge volumes of ore being produced from the Garrison Mine, the richest of the early mines. The camp's population swelled to more than 400. A post office, with James Russell as postmaster, opened on January 3, 1868. In 1886, Wenban built a 50-ton leaching plant at the Garrison Mine. The mill continued to operate until 1894. From 1887 to 1891, the Cortez mines produced over $300,000.

By the late 1920s and early 1930s, however, silver prices dropped dramatically and activity in Cortez slowed down. The mill was shut down in January 1930, and the company finally folded a couple of years later. Today the property is controlled by Placer Amex Incorporated and the mining and milling operations continue.