English: Volcanic ash, pumice deposits, and lava flows in the Quaternary of Orgeon, USA.

Shown here is Llao Rock, the most distinctive cliff-face along the rim of the caldera. The tan-colored material at the top is a mix of rhyodacite pumice and ash deposited during the caldera-forming eruption at 7.7 ka. This material was deposited as pumice fall and ash fall throughout much of America's Pacific Northwest and southwestern Canada.

The grayish-colored rocks making up most of the cliff are part of the Llao Rock lava flow, which erupted ~7,800 to 7,900 years ago, not long before the caldera-forming event. This is a single lava flow erupted from a vent located here at Llao Rock. The maximum reported thickness of the Llao Rock lava flow is 1,200 feet. The rocks are composed of rhyodacite (also referred to as felsite) and usually have ~70.5% total silica. About 7% of this rhyodacite lava consists of small phenocrysts composed of plagioclase feldspar, hornblende amphibole, orthopyroxene, iron & titanium oxide minerals, and augite pyroxene. The lava's groundmass is finely-crystalline (aphanitic). Masses of darker-colored andesite are common in this unit.

Between the base of the Llao Rock rhyodacite lava flow and lake level is a series of older volcanic deposits. These consist of five Pleistocene andesite, basaltic andesite, and dacite lava flows. They range in age from ~42 ka to ~137 ka.