My Gx3 Grandfather, John Hopkins of Portsmouth New Hampshire came to the ranching area of Rancho San Jose(near current day Pomona/Ontario) around the time of the goldrush. My Gx2 grandfather, George Hopkins was born in Rancho San Jose in April 1853 (his mother was a Mexican woman of very poor means--Maria Martinez). What baffles me is that while the population in San Francisco was exploding and there were 100s of thousands of 49ers in the hills, bay and Delta, the south was only populated by Mexican settlers from the Spanish colonial era and what remained of the native population. From what I've read the LA census was something like 2k people almost entirely Mexicans. Why the hell would this ancestor (or anyone really) have chosen to go to SoCal vs NoCal during this time? Cattle? Gold? Military? Trade? Adventure?
I'm especially interested in any primary source material that I could use in researching the context and possibly my family members that may give a clue. The 1852 census doesn't help in my case. I'm in the Bay Area and have looked at some stuff in the Bancroft Holdings at Berkeley as well as some of the digitized stuff online at various libraries.
In the entire family tree of American gold rushes (of which California is the trunk), there were men and women who realized that money could be made buying and selling to the miners, rather than doing the mining themselves.
Some of these men and women simply worked as porters, hauling supplies to and from mine sites. Labor was always needed, particularly in the early stages of a gold rush, when heavy equipment had not yet arrived on scene, either through lack of availability or lack of investment.
There were the vendors too, men and women who sold supplies or services. These could be physical, as in the case of dance halls and hotels, or logistical, in the case of stores and equipment, to name just a handful of examples.
One thing a gold rush boom always brought was a scarcity of food. A surge in an area's population almost always outstripped the ability of that area to feed the newcomers. I'm thinking in particular of the infamous first winter of Dawson City, when starvation was barely averted and forced the Northwest Mounted Police to require newcomers to carry supplies into Canada as they arrived.
While the Yukon would come later, the same was true 50 years before in the California Gold Rush of 1849. As thousands of miners arrived, there was hunger. Food prices skyrocketed. The rich agriculture of Oregon supplied some of the demand, but thanks to transportation charges, costs were high. That made local agriculture a particularly lucrative business, if someone could be distracted from the goldfields.
It's possible that your great-great-great-grandfather followed a path that many gold rush miners did ─ no matter whether it was in the Yukon or California. Ninety-nine percent of the men who traveled to those places never struck it rich through mining. Many were so disgusted by the hardships and cruelty of the mining industry that they abandoned it.
Some returned home. In the case of the Yukon, most did. In the case of California, many stayed ─ attracted by the pleasant climate, abundant land and fertile (in well-watered places) soil.
For Alaska, Ann Chandonnet's Gold Rush Grub: From Turpentine Stew to Hoochinoo is a good source that I can recommend. It also contains references to prior gold rushes, including California. You might also try Conlin's Bacon, Beans, and Galantines: Food and Foodways on the Western Mining Frontier, which I haven't read in a long time, but I recall has ample discussion of how the miners were fed in California.