The oldest rocks within the district are present to the west of the southeast-dipping Comstock Fault and include the Triassic to Jurassic Gardnerville Formation, meta-igneous rocks of inferred Jurassic age, and Cretaceous granitic rocks of the Sierra Nevada Batholith. These older rocks are successively overlain by Oligocene rhyolite ash-flow tuffs and predominantly andesitic flows and intrusions of the Miocene Silver City and Virginia City volcanic suites. Miocene-age Davidson diorite is most commonly present west of the Comstock Fault in the northern part of the district but has also extensively intruded the Virginia City suite of volcanics, older rocks in the footwall, and the Comstock Lode itself. The andesitic flows of the Kate Peak Formation, which comprises the upper member of the Virginia City volcanic suite, are present to the east, adjacent to the Occidental-Brunswick Lode. The key element of the district from an economic standpoint is the complex system of faults that host mineralization. Most of the structures are moderately dipping (down-to-the-east) normal faults with displacements of up to 300 meters. The Comstock Fault, which is the most significant structure in the district, forms a mineralized zone which is locally up to 245 meters wide that extends more than 5,400 meters along strike through Virginia City in the north and Silver City to the south. Both the Comstock and Silver City lodes are hosted in this continuous zone. Mineralization has been detected to depths of more than 3,000 feet on the Comstock Lode proper.