Geology Reference
In-Depth Information
Oceanic environments associated with the major
Blue Mountains exotic accreted terranes
units, it is impossible at present to associate details of
this suite of ancient rocks to the rest of the rocks in
the Blue Mountains. Clues to the origin of the Grind-
stone terrane are evident in the similarity of rocks and
fossils of the Coyote Butte Formation to the Bilk
Creek exotic terrane north of Winnemucca, Nevada.
The diversity of formations in the Grindstone
terrane make up what is called a mixture or melange of
rocks. Interpreted as once forming the boundary
between two converging crustal blocks, melanges are
areas where different geologic environments have been
telescoped or jammed together by the colliding plates.
As with the Olds Ferry and Wallowa terranes, the
Baker and Grindstone terranes have sometimes been
combined because of similarities between the melanges
in them. The position of the Grindstone on the west-
ern side of the Izee terrane seems to support this but,
contrasting rocks between the two terrances would
argue against it.
Fishtooth-like microfossils, conodonts from the
Devonian limestone in the central Oregon Grindstone
terrane, are less than 1/32 inch in length (courtesy of
N.M. Savage)
