The Arica district, in the Arica Mountains of northeastern Riverside County, also has been known as the Onward district. The Brown and Lum-Gray mines, the principal sources of gold, were active during the early 1900s and again in the 1920s and 1930s. A number of gold-quartz veins occur in granite and schist. Sulfides are extremely abundant, and the milling ore was reported to have yielded as much as one ounce of gold per ton. The Lum-Gray shaft is nearly 1000 feet deep.
Merrill, F. J. H., 1919, Riverside County, Arico Mountain district: California Min. Bur. Rept. 15, pp. 541-542.
Tucker, W. B., and Sampson, R. J., 1945, Riverside County, Brown and Lum-Gray mines: California Div. Mines Rept. 41, pp. 128 and 138.