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Stop 17, Shoo Fly Complex: The Setting

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Stop 17 is at 40°01.894´N, 121°00.891´W at another tight pullout on route 70. (more below)
Cambro-Ordivician metasediments
Photo (c) Andrew Alden, licensed to About.com (fair use policy)
The Shoo Fly Complex contains the oldest rocks in the Sierra Nevada, of Ordovician or Cambrian age (400–500 Ma). It consists of typical metamorphosed sedimentary rocks: quartzite (formerly sandstone), phyllite (formerly shale) and chert. This outcrop appears to show turbidite sequences, alternating sandstone and shale like the Great Valley Group sequences we saw between stops 4 and 5, but altered by heat and pressure. This group of rocks is thought to be exotic, that is, formed elsewhere and carried here by plate tectonics. It may have formed near western Gondwana (the modern African plate) or eastern Laurentia, on the opposite side of the North American plate. If that seems strange, consider that similar chunks of land have been carried up the North American west coast to Alaska and points between, where they are mapped as "exotic terranes." Outside the ancient central parts of the continents—the cratons—much of the world's continental rocks have been shuffled and rearranged for billions of years.

Stops 17 through 19 are in the Eastern Belt of the Sierra Nevada, as are stops 24 and 25.

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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