The Putah Tuff is approximately 1.8 million years old, the product of volcanic eruptions to the west as the San Andreas fault zone rearranged the crust of the Coast Ranges. Today the corresponding volcanism is around Clear Lake and The Geysers about 100 kilometers to the north. Tuff is a conglomerate of volcanic ash and rocks. Here it is interbedded with the Tehama gravel, whose sediments come from the Coast Ranges to the west.
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