The late 1800s were a time when gold was mined by large corporations using high-pressure water jets to sift huge beds of gold-bearing (auriferous) gravel. This practice permanently altered the Central Valley by covering it in sterile silt, destroying many riverbeds in the process. A federal judge set the basis of environmental laws by declaring the worst practices illegal in 1884, but less disruptive hydraulic mining continued well into the 20th century in, for example, the Tuolumne River valley.
The story goes that miners' hoses chewed away all of the Eocene (50 Ma) auriferous gravels of the Yuba River valley until they reached the land owned by the railroad, which refused to sell, thus leaving a high ramp of undisturbed gravel under the tracks. A little west of here, I-80 passes a dramatic exposure of the gravels—but of course there is no stopping on the interstate.
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