Section from the piston core YL92-1C, collected in south-central Yellowstone Lake
Section from the piston core YL92-1C, collected in south-central Yellowstone Lake. The core is viewed horizontally, with the top of core to the left. The core section shown is from 5.21–5.63 meters (17–18.4 feet) depth. The 0.5 centimeter (0.2 inch) thick white Mazama ash, from the eruption that resulted in the formation of Crater Lake in Oregon, is clearly identifiable and provides a marker bed of known age (7,700 years old). About 29 centimeters (11 inches) below the Mazama ash is a 5 centimeter (2 inch) thick deposit of the Elliott’s Crater hydrothermal explosion (about 8,000 years old) where hydrothermally altered minerals including quartz and clay minerals chlorite and smectite are found.