The Calico Mining District is located in the Calico Mountains, California. The sequence of exposed rocks in the District filled the Calico Basin during the Miocene. An excess of two-thousand feet of the andesitic Pickhandle Formation is uncomformably overlain by 2,500 feet of rhyolitic to Andesitic epiclastic rocks of the Calico Formation. A few thousand feet of variable colored lacustrine deposits of the Barstow Formation conformably over the the Calico Formation, Andcsitic to basaltic flows and flow breccias of the Dry Lake Volcanics unconformably overlie the Barstow Formation. Formation of northwest-trending antithetic faults, at intervals of five-hundred to one-thousand feet, accompanied a general doming of the Calico Mountains. Intense folding of the Barstow Formation Resulted from the lake beds sliding off the doming surface. Ores of silver chloride and other halogens of silver from the zone of oxidation produced 35 million ounces of silver from 1898 to 1894. Silver deposits in the District are of two types: 1) vein-fault systems consisting of cerargyrite in a barite hematite-red jasper gangue or as cerargyrite-hematitie cement in fault breccias, or 2) as deposits of irregular form often associated with a fault and bedded tuffs. Recent investigations indicate the ore bodies are stratabound primarily restricted to the Calico formation. Since the early 1890s, the ore has been considered hydrothermal in origin. A syngeneic origin is now proposed.