Geology Reference
In-Depth Information
The Great Basin portion of the Basin and Range
province barely extends into southeast Oregon.
Geologic Overview
The Basin and Range is a tectonically youthful
province with an anomalously high heat flow, thin
outer crust, and a high regional elevation. The most
pronounced structural phenomena effecting the Basin
and Range province are the stretching or extension of
the crust and the movement of large tectonic blocks.
These forces are responsible for giving the basin its
characteristic tilted, raised mountains and down-
dropped basin structure as well as producing the
volcanic activity of the late Tertiary. A complex net-
work of faults and fissures resulted as the enormous
crustal blocks were uplifted, tilted, or dropped while
the basin was being stretched and distorted. Major
faults are marked by spectacular scarps trending
northward along the face of the mountain ranges.
Cenozoic volcanic activity in this province
began in the Miocene and continued into the Pleisto-
cene resulting in basalts, tuffs, and tuffaceous sedi-
ments totalling nearly 10,000 feet in thickness. As the
crust thinned and cracks appeared, magma from below
broke through to cover the area. Basalts and ash were
extruded from a broad shield volcano in the region of
Steens Mountain. Following this a number of large
calderas in the southeastern part of the state were
