Geology Reference
In-Depth Information
Miocene time. The Blanco and Mendocino fractures
are the source of an ongoing series of magnitude 5 and
6 earthquakes in southwestern Oregon and northern
California. Although the quakes have occasionally
moved houses off foundations, to date no catastrophic
damage has occurred. Some commercial interest has
been shown in the offshore spreading centers for their
mineral potential, but technology, economics, and
environmental considerations may temporarily preclude
the exploitation of these massive sulfide deposits.
slope, and tilting phenomena all suggest a close rela-
tionship between uplift of the Coast Range block and
the subducting slab of the Juan de Fuca tectonic plate
beneath the North American plate.
Structurally the Coast Range is a large crustal
wrinkle with a north-south axis. The terms anticlinori-
um and synclinorium are used to describe extremely
large folds of this type with many smaller crenulations
across the flanks or limbs. At the north end of the
coastal mountains the Willapa Hills of southwestern
Washington is an upfold or arch that crosses the
Columbia River into northeast Columbia County. Just
south of the river at Mist, rocks of the coast are domed
into a low anticline at the Nehalem arch. To the
southwest, this fold becomes the Tillamook highlands.
Structure
Evidence throughout the Coast Range reflects
the ongoing uplift of the entire province. Rock frac-
tures, faulting and folding, terraces on the western
Search WWH ::




Custom Search