Geology Reference
In-Depth Information
Vertical sequence of the Joseph-
ine ophiolite in the Oregon
Klamath Mountains (after Harper,
1984; Harper, et al., 1985)
Northwest of that region, the Greyback belt of
late Jurassic age includes the large Greyback pluton as
well as the smaller Gold Hill and Jacksonville plutons.
This belt, dating back to 153 million years ago intruded
the Hayfork, Rattlesnake Creek, and May Creek
subterranes of the Western Paleozoic and Triassic belt.
Just northwest of the Grayback belt, the Grants Pass
early Cretaceous plutonic belt at 140 million years
includes the large Grants Pass and White Rocks
plutons. Displaying 85 degrees of clockwise rotation,
the Grants Pass plutons intruded the Smith River
subterrane on the south and the Rattlesnake Creek and
Rogue Valley subterranes to the north after amalgam-
to those covering over 100 square miles. Intrusives are
situated in four major northeast trending belts with the
oldest in the southeast and the youngest in the north-
west. The oldest of these, the Wooley Creek belt of
late middle Jurassic age at 155 million years ago
includes the Ashland plutonic complex of quartz
monzonite and granodiorite. About 150 square miles in
total size, approximately two-thirds of the Ashland
pluton is in Oregon where Mt. Ashland is its major
exposure. The Wooley Creek pluton belt intruded the
Rattlesnake and Hayfork subterranes of the Western
Paleozoic and Triassic belt terrane after the subterran-
es had been amalgamated.
