This law, approved on May 10th, 1872, codified the informal system of acquiring and protecting mining claims on public land, formed by prospectors in California and Nevada from the late 1840s through the 1860s, such as during the California Gold Rush. A mining claim is the right to explore for and extract minerals from a tract of land. FOR SALETwo 20-acre placer BLM mining claims in Baker County, Oregon. Located in an established placer gold district. Located in an established placer gold district. Established reserves at a very conservative 22,000 cubic yards at a grade of 0.58 grams (0.0186 ounces per ton).