Those correct dates are from 1860-64 and he was working for the US Geological Survey under Josiah Whitney (it is available online here). His diary (I have it in front of me) emphasizes a particularly wet set of years due to the great flood of January 1962, which would skew his observations for years thereafter. If I recall correctly, he went down to the southern Sierra the year after the flood.
You are right it has been twenty years since I read it. The title fits the narrative. A whole lot of going up and down mountains. Pretty dry reading if I remember.
Still, my point is there was a lot of surface water throughout California early on. Especially if you believe the maps the greenies use to show how much wetland has been “lost”
The pacific is the great provider of moisture. The coastal ranges may be damp but extract little in my opinion. I absolutly love Sierra thunderstorms when they happen.