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.