Volcanic ash (or tephra) originating from the eruption of Mount Mazama (Crater Lake, Oregon) nearly 7000 years ago (6600 years ago). Undisturbed beds of Mazama ash provide important contextual dates for archaeological sites throughout the northwestern United States and southwestern Canada. The eruption also produced Crater Lake in Oregon. Great thicknesses of pumice were deposited on the flanks of Mount Mazama, while finer material was blown over great distances by the winds. The widespread distribution of the Mazama Ash has made it useful in archaeological studies as a horizon, or time, marker. Studies of sediments formed in relation to the ash deposits suggest that the ash formed at a time when generally drier climates prevailed in the regions in which the ash occurs. The mineralogical composition of the ash is distinctive and allows it to be distinguished from other volcanic ash deposits.