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Stop 4, Sedimentary Serpentinite: The Setting

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Stop 4 is at 38°30.485´N, 122°12.858´W above an arm of Lake Berryessa on Spanish Flat Road. (more below)
A grassy roadcut
Photo (c) 2006 Andrew Alden, licensed to About.com (fair use policy)
This stop is rather overgrown, and I found it hard to find the features described in the guidebook. That is something to be mindful of with any published field-trip guide—vegetation may grow and exposure may degrade the quality of the rock.

The middle part is serpentinite, and it is said to lie on top of sedimentary rocks of the Great Valley Group. The Great Valley Group is a huge thickness of sandstone and shale representing the forearc, the wedge lying between the trench and the volcanic arc. This section of serpentinite may have erupted through the wedge as mud volcanoes, unlike other serpentinites that represent more deeply subducted oceanic crust.

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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