gems, USA, California, San Diego County, Pala, Stewart Lithica mine, pegmatite, tourmaline, geology, Himalaya Mine

The Pala pegmatite district in northwestern San Diego County, California, has long been recognized as a significant source of gem and lithium minerals. Although formal mining began in the 1870s, the district’s peak production occurred between 1900 and 1922. By 1947, total recorded output was valued at approximately three-quarters of a million dollars, including 23,480 short tons of lepidolite, 2,180 pounds of tourmaline, and 1,325 pounds of gem spodumene, along with minor quantities of amblygonite, beryl, feldspar, and quartz. Six major mines were heavily worked for lepidolite and gem minerals, with many smaller deposits also explored. The district lies within the southern California batholith of probable Cretaceous age, interspersed with older schists and quartzites as septa and pendants, and partially covered by Quaternary surficial deposits. Over 400 pegmatite dikes are exposed across a 13-square-mile area, most trending north and dipping west at gentle to moderate angles. These dikes vary greatly in size and continuity, often forming swarms of subparallel bodies that may branch, converge, or merge into thick composites while retaining distinct identities. Primarily emplaced in gabbroic host rocks, the pegmatites appear to follow a system of fractures unrelated to the primary structure of the surrounding rocks, crossing lithologic boundaries and suggesting emplacement along subhorizontal zones.