Mazama Ash

The Mazama Ash is a large geologically recent volcanic ash deposit that covers portions of the U.S. states of California, Oregon, Washington, Idaho, Montana, Nevada, Wyoming and Utah, as well as the Canadian provinces of British Columbia, Alberta and southwestern Saskatchewan. It was created by a massive explosive eruption of Mount Mazama ~6,900 years ago, during which it collapsed to create the caldera of Crater Lake.

To the south, the Mazama Ash overlies the older Bishop Tuff. To the north, it is overlain by the 508-year-old Wn Ash and the 3,400-year-old Yn Ash from Mount St. Helens, as well as the 2,400-year-old Bridge River Ash from Mount Meager.