Within the regional area, there are a series of well-defined caldera ring structures;
these are clearly visible on Landsat imagery and air photos. These features range in
size from 7 km to 12 km across and are nested within less well-defined volcanic
complexes. Felsic (rhyolite dominant) units predominate to the northeast, east and
southeast of the Project, while intermediate rocks predominate to the west and
northwest.