Historic Resource Study, Crater Lake National Park, Oregon, 1984
V. Geological and Biological Information on Crater Lake Area
E. Points of Geological Interest in Crater Lake National Park
6. Llao Rock
This great mass of dacite (a sluggish lava) was produced from a vent somewhere on the upper slopes of Mazama and hardened after moving only a mile or two. The dacite filled in a former explosion crater. This rock rises nearly 2,000 feet above the water–the highest vertical precipice on the rim- -and was formed by the most massive single flow apparent in the caldera wall, with a maximum thickness of 1,200 feet.