These volcanic rocks are encompassed by an oval-shaped zone of late Cenozoic ring faulting that measures about 24 miles (39 km) east to west and 28 miles (45 km) north to south and that defines a structural basin.

Most of the Coso Range and a slice of the adjacent Sierra Nevada lie within this ring structure.

The youngest volcanic rocks are Pleistocene and, with associated active fumaroles, occupy a north-trending structural and topographic ridge about 11.2 by 6.2 miles (18 by 10 km) near the center of the basin.

The ring structure and associated volcanic rocks suggest a large underlying magma chamber that has periodically erupted lava to the surface during the past few million years.

The prehistoric Coso inhabitants exported volcanic glass (Coso obsidian) and this highly valued toolstone has been found as far distant as the Channel Islands of California.