Llao Rock
17. The great cliff at Llao Rock (Panorama D), which dominates this aerial view looking northwest, slices into Holocene rhyodacite lava (unit rh) that filled and overflowed the explosion crater formed in the early stages of the same eruption. Ash from the explosive phase of this eruption (unit rhp), which occurred 100-200 years before the caldera-forming climactic event, is found as far away as northern Nevada and northeastern California. Climactic pumice fall (unit cp) rests on the craggy top of the lava flow but was stripped from its lower flanks by pyroclastic flows of the ring-vent phase of the climactic eruption. Several lava and pyroclastic units exposed in the caldera wall below Llao Rock range in age from unit all (~140-170 ka) to unit asb (436 ka here). The broad shield volcano (lowest third of wall), composed of units all and alu, and the thick wedge of unit am (left) are clearly visible.
Photograph by Charles R. Bacon.