Geology Reference
In-Depth Information
Major structural features of the Blue Mountains in
northeastern Oregon
running across the northeast corner of the province are
the Grande Ronde lineament and the Olympic-Wallo-
wa lineament. The Grande Ronde alignment parallels
Eagle Creek and the upper Grande Ronde valley for
miles across eastern Oregon. To the southwest the
Olympic-Wallowa lineament, a very straight structural
trend extending across the Columbia plateau and
northern Blue Mountains, connects with the Vale and
Snake River fault zones.
to fold upward around 35 million years ago in early
John Day time. The development of this structure
correlates with the breakup of the Farallon plate
between the Murray and Mendocino fracture zones in
the Pacific Ocean and records a strong north-south
compression. Running parallel to and only slightly
southeast of the Klamath-Blue Mountains lineament,
the Blue Mountains anticline may mark a deeply buried
suture between two microplates in the crust below.
A number of extensive large-scale lines or
lineaments across Oregon are of such magnitude that
they are seen best on high altitude aerial photographs.
The cause of the lineaments is not understood, al-
though they apparently represent a boundary or
structure buried deep in the crust. These lineaments
are traced along interconnected faults and folds or
more subtle features such as the alignment of straight
stream valleys. In the Blue Mountains, two lineaments
Mining and Mineral Industry
Gold
The region of the Blue Mountains has pro-
duced about three-fourths of all of Oregon's gold.
These deposits occur in the gold belt of the Blue
Mountains, so named by Waldemar Lindgren. The strip
