HARTMAN MULTIMEDIA
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HARTMAN MULTIMEDIA
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Cucamonga Canyon In the Cucamonga Canyon there is an excellent display of
mylonites and granulites, along with the structural features present from the
deformation of the rocks. Mylonites
are fine-grained rocks formed by extreme crushing and milling during strong
deformations, often during movement on fault surfaces. Granulites are
metamorphic rocks originating in high, confining pressures and temperatures in
the range of 700-800° C. They may be
products of a secondary metamorphism from an earlier amphibolite-gneiss
complex. These mylonites indicate that the San Gabriel Mountains
are among the most fractured and shattered in the State.
The oldest rocks in the area are pre-Cretaceous in age and are granulites
that have been folded. Where they
have been faulted, they have become altered mylonites.
There are a number of metamorphic and igneous structures formed in the
rocks, with numerous examples of faulting and frequent intricate folding. Integrity: Aside
from a trail in the canyon, the area is virtually undisturbed. Use: Research,
educational, observational. Ref: Hsu, K.
J. 1955.
Granulites and Mylonites of the Region about Cucamonga and San Antonio
Canyons, San Gabriel Mountains, Calif. Univ.
of Calif. Publ. in Geol. Sci. Vol. 30, No. 4, pp. 223-352. September 1976
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