The Comstock Lode is a lode of silver ore located under the eastern slope of Mount Davidson, a peak in the Virginia Range in Virginia City, Nevada (then western Utah Territory), which was the first major discovery of silver ore in the United States and named after American miner Henry Comstock. After the discovery was made public in 1859, it sparked a silver rush of prospectors to the area, scrambling to stake their claims. The discovery caused considerable excitement in California and throughout the United States, the greatest since the California Gold Rush in 1849. Mining camps soon thrived in the vicinity, which became bustling commercial centers, including Virginia City and Gold Hill. The Comstock Lode is notable not just for the immense fortunes it generated and the large role those fortunes had in the growth of Nevada and San Francisco, but also for the advances in mining technology that it spurred, such as square set timbering and the Washoe process for extracting silver from ore. The mines declined after 1874, although underground mining continued sporadically into the 1920s. Geology Volcanic vents to the east covered the area during the Tertiary, and a fault fissure opened the east slope of the Virginia Range. The east slope of the range forms the footwall of the Lode, and is composed of diorite, while the hanging wall is composed of andesite, which the miners called "porphyry". The fault fissures filled these fissures with "mineral-bearing quartz". The miners stated "porphyry makes ore". The ore bodies were thinly scattered through the wide Lode "like plums in a charity pudding", and nearly all of them were found in the wide upper section and along or near the east wall. Although the miners extended their work in all directions, only "sixteen large and rich ore bodies" were found, most less than in depth. Bonanzas Six major bonanzas marked the first five years of the Comstock Lode. The Ophir bonanza was prosperous until 1864, producing 70,000 tons. Though rich, and having a length of at the surface, the ore body wedged out at a depth of . The Gould & Curry bonanza included of the El Dorado outcrop, but dipped southward into the Savage at ; the ore gave out by 1866. The Savage bonanza included this ore body and a second bonanza, an ore body shared with Hale & Norcross to the south, at the 600 foot