Regional Report: Gem Hill, Mesa Grande District, San Diego Co., California, USA

Gem Hill is a gentle sloping geographic feature with an elevation of approximately 4058 feet above mean sea level (AMSL). The hill was named by local residents in recognition of the fabulously rich gemstone discoveries of tourmaline and beryl which were made in the area beginning in the late 1890's. The hill area primarily consists of gabbroic country rock, and hosts several gem-and-rare earth element (REE) and lithium-cesium-tantalum (LCT)-bearing pegmatite veins or dikes that outcrop as ledges which follow a general northwest trend. Several of these pegmatites have been prospected for gemstones with small cuts and trenches, or developed underground by extensive subsurface workings exceeding 300 feet in depth. The most heavily worked pegmatite deposit in the area is the famous Himalaya dike system.

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