Air fall ash beds (Pearlette) originating from rhyolitic eruptions in the Yellowstone-Island Park region of Wyoming and Idaho are discontinuous but widespread throughout the western United States. Accumulation and deposition of ashes occurred in low-energy fluvial and lacustrine environments. These ash beds have been correlated, according to their chemistry and remanent magnetism, with specific eruptions of tuffs of the Pleistocene Yellowstone Group.