One of the great blog projects for the geologically minded reader is "Up and Down California," which serializes the government-sponsored Whitney Survey exactly 150 years later. The survey was a remarkable four-year-long expedition led by Josiah Whitney (eponym of Mount Whitney), mapping and describing the mines and geology of the new state of California.
In yesterday's entry (that is, on 13 August 1862), Whitney describes the state of the Sacramento River after two mammoth disturbances: first was the widespread hydraulic mining of the Sierra Nevada gold country, which stripped whole landscapes of their forests and soils; second was the terrible wet winter of 1861–62, when six solid weeks of "atmospheric river" rain redeposited much of the Sierra's loose sediment and massively flooded the Central Valley. "Indeed," Whitney writes, "the water is still over a part of it." He describes drastic changes in the rivers feeding into the Valley, changes that are still felt today.
The situation of California 150 years ago was one of the first, if not the first, instances of human activity pervasively altering a region. Today that premonitory example has been magnified to the entire globe, as the atmosphere itself is rushing toward a doubling of its carbon-dioxide levels and the world's temperature steadily rises. That situation, in which the human race finds itself at the wheel of the world, is called the Anthropocene age. Josiah Whitney was a scientific witness to one of its first stirrings.
Related:
California's Great Central Valley
The gold rushes
Introducing the Anthropocene
Comments
The Central Valley is still prone to flooding in years with much rain. When driving east across the Valley on Hwy 20 one winter in the 90s I had to detour about 50 miles south around a flooded area. A week later I was able to drive back on the normal route. On both sides of the road there was essentially a shallow lake of many miles width. Visible here and there across the tranquil surface were trees, farm buildings, power lines, etc.
I assume that the Valley has always been relatively flat. Its inherent flatness probably made it especially prone to interruption of natural drainage patterns by accumulation of placer waste. Perhaps it has been made flatter recently by grading to develop agricultural fields, particularly rice fields.
Also I’d like to suggest that flooding in the Valley may have value in recharging ground water.