reports of oil seeps on the peninsula and on the cape between aniakchak and amber bays in the 1920s brought petroleum exploration and claims, some of which described the "aniakchak field." detailed surveys established that the seeps did not exist, and that much of the region was composed of non-oil-bearing igneous rock, ending speculation. the reports did provoke interest from the u.s. geological survey, and in 1922 and 1925 usgs parties surveyed the region. these surveys brought the first detailed accounts of what they described as an "extinct volcano," of which fragmentary information had only emerged after 1919. however, in 1931 half cone, one of the cinder cones in the caldera, erupted throughout may of that year, causing ashfalls at distances up to .