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Stop 29, Cordelia Fault: The Setting

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Stop 29 is near Fairfield at 38°15.196´N, 122°08.145´W on Rockville Road where it cuts across the Cordelia fault. (more below)
Best-exposed fault of the San Andreas group
Photo (c) 2006 Andrew Alden, licensed to About.com (fair use policy)
The rocks west of Fairfield include large exposures of the Sonoma Volcanics, erupted in the Pliocene and Quaternary after about 6 Ma. These rocks are part of a northward trend of volcanism related to the switch from subduction to transform motions as the oceanic plates west of North America were reorganized. The Cordelia fault is part of the San Andreas fault system, possibly a branch of the Green Valley fault we saw at stop 3. Active as recently as the Holocene Epoch (since 10,000 years ago), this locality is the best exposed strand of the San Andreas system in northern California.

Tuff from this spot, the east edge of Green Valley, is included in the gallery of extrusive volcanics.

Day 1, Coast Range: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

Day 2, Sierra Nevada: 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18

Day 3, Sierra Nevada: 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28

Day 4, Coast Range: 29 | 30 | 31 | 32 | 33

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