Black Forest landslide boulder, Clear Lake Volcanic Field

A prominent feature carved out of the side of Mount Konocti is the Black Forest landslide, which occurred on the eastern side of Buckingham Peak and deposited massive boulders down near the shore of Clear Lake. Determining when the landslide occurred is difficult, but two broad age constraints do exist. The first comes from the youngest of the massive dacite boulders in the slide, which are from an ~ 400 kyr old rock unit called the Dacite of Buckingham Bluffs. Inclusion of these blocks in the slide indicates that the feature is no older than these rocks. The second constraint is provided by the ~ 10 kyr old maar crater containing Little Borax Lake. When this maar erupted to form the crater, it cut through existing landslide deposits, which indicates that the slide is older than 10 kyr. This photo shows a block of dacite that tumbled down toward Clear Lake as part of the Black Forest landslide. USGS photo by Jessica Ball.