Diamond Craters in southeastern Oregon is a monogenetic volcanic field about 40 miles southeast of Burns, not a single mountain but a 27-square-mile expanse of basaltic lava flows, cinder cones, and maars. Evidence from radiocarbon dating and paleomagnetic study places its eruptions between 7,320 and 7,790 calendar years before present. The name comes from the Diamond Ranch, founded by pioneer Mace McCoy, whose livestock bore a diamond-shaped brand. In the 1970s, illegal removal of lava slabs for building veneer raised alarm among geologists, and in 1982 the area was designated an Outstanding Natural Area for its scientific value and fragility.