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Stop 18, Peale Chert


This stop is at 40°09.350´N, 121°05.289´W on Seneca Road overlooking the North Fork Feather River canyon. (more below)
Earlier version of stop 1 chert
Photo (c) 2006 Andrew Alden, licensed to About.com (fair use policy)
The Peale Chert spans an age range of 359 to 271 Ma, from the Early Mississippian to Early Permian epochs, yet is less than 100 meters thick. It is very much like the Franciscan cherts of the Marin Headlands at stop 1 in this respect, and we can surmise that a wide expanse of deep sea floor was once subducted here beneath western North America in the late Paleozoic just as it was farther west during the Mesozoic.

The other attraction of stop 18 is recent flows of basalt, less than a million years old, that represent the latest volcanism in the northern Sierra Nevada. Several basalt flows went down the North Fork Feather River valley here from eruptive centers near Lake Almanor. The river quickly cut through the flows to resume its former course, but remnants remain as terraces along the sides of the canyon that give evidence of recent fault movement in this part of the Sierra. Just north of here begins the Cascade Range province, the site of vigorous volcanism today related to the current subduction of the Pacific plate beneath North America.

I had a lot of trouble at this stop, and I was forced to conclude that the GPS location in the book is wrong. Fortunately there is more than one place to observe both the Paleozoic chert and the Pleistocene basalt if you don't go too far past this spot.

This is the last stop of day 2. The field trip suggests an overnight stay in Quincy, and I can recommend that too. Day 3's stops go southward along the Sierra crest, then west down the Yuba River valley to the foothills again.

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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