When I randomly recall old wealth families that I’m aware of, they pretty much all started from local business tycoons (newspapers, railroads, essential consumer products, etc.) that usually diversified through real estate. No different than the rest of the US.
It is the gateway to asian trade, Mediterranean climate, resource rich, has great ports, chokepoints east that make scaling business like railroads easier, etc. It was also empty during modern times.
Except for all of the people who lived there. https://en.wikipedia.org/wiki/Indigenous_peoples_of_Californ...
"Prior to European contact, California Indians had 500 distinct sub-tribes or groups, each consisting of 50 to 500 individual members."
Assuming that all 500 tribes were 500 people, that's only 250,000 people. Relative to the geographic size of the state, that's a pretty low population density. And many of the the areas of large growth wouldn't have been useful to a pre-industrial civilization, since they required so much labor and technology to exist (like say, pumping in water from 4 neighboring states in order to meet the needs of the population).
Let's settle on "It had a relatively low population of Indigenous people to area" instead of "it was empty", and call it a day?
They certainly weren't treated well, and I make no excuses for that, but the place was essentially empty by the time California started hockey-sticking.
That same defense contract money and influx of tech talent is largely responsible for the foundations of Silicon Valley as we know it today.
Agriculture and railroads followed the gold.