Pinnacles Nat. Mon November 2011
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© W.P. Armstrong 24 November 2011
Approximately 25 million years ago the Pinnacles Volcano was born along the contact zone (strike-slip fault) between the North American and Pacific plates. Its original latitude was near present-day Lancaster in the Mojave Desert of southern California. It moved slowly northward along the San Andreas Fault to its present location in coastal central California. At its maximum size it was about 25 miles long, five miles wide and 8,000 feet high, slightly smaller than today's Mount St. Helens in southern Washington. Dissected by faults and earthquakes, frost wedging along joints, and millions of years of erosion; it was gradually transformed into massive rock monoliths and spire-like pinnacles separated by steep rock walls, ravines and deep caves. Most of its volcanic rock is rhyolite, in marked contrast with the surrounding Coast Ranges. Unlike the dark basaltic volcanic rocks of Hawaii and many parts of the western United States, rhyolite is high in silica, making it both light-colored and nonporous. The massive rock formations are colored black, green and red by numerous species of crustose and foliose lichens. Shady, moist rock faces are covered by dense colonies of bright green mosses, with beautiful ferns in the crevices.

The Following Images Taken With Sony DSC-TX5 in Hand-Held Twilight Mode

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