In the western United States and Canada, volcanic ash often forms distinct layers among recent geological deposits, which can be used for stratigraphy among geologists and archaeologists. Given the large distribution of the historic eruption of Mount Mazama, Mazama Ash serves as a common geological marker. Mazama Ash had a minimum fallout area of , while ash from the nearby Glacier Peak volcano, known as Glacier Peak Ash, encompassed an area of more than . Mazama Ash is found at a higher layer than the Glacier Peak ash, estimated to have deposited over 13,000 years ago. Mazama Ash is the most widely distributed tephra layer from the late Quaternary in the United States and southwestern Canada, extending to eight states to the west and three Canadian provinces. Mazama Ash forms orange colored deposits.