Geology Reference
In-Depth Information
Hole-in-the-Ground, near Fort Rock, is a remarkable explosion crater (photo courtesy of Oregon Dept.
Geology and Mineral Industries).
the top of a large block which fell into the depression
during the eruption. Unlike Fort Rock and Hole-in-
the-Ground, Big Hole is heavily forested. The trees and
its immense size make this volcanic feature difficult to
visualize from the ground level.
Four Craters, Devils Garden, and Squaw Ridge Lava
Fields
Continuing Pleistocene volcanic activity in the
eastern High Lava Plains resulted in a number of
unusual lava flows, domes, pumice and cinder cones,
and lava tubes at three locations in Lake County. At
Four Craters Lava Field on the northern edge of
Christmas Lake Valley, four cinder cones with smaller
mounds are surrounded by lava flows emitted from
vents aligned along a fissure. Here blocky and broken
aa lava from the cones covers about 12 square miles.
Nearby Devils Garden and Squaw Ridge lava fields are
At Hole-in-the-Ground, the collapse blocks and cra-
ter rim are overlain by a thick layer of ash and tuff.
(modified after Peterson and Groh, 1961)
