I'd need to dig it up again, but I had read a journal article that there's evidence that the maize cultivation along the lower Colorado River had spread to the coastal region as a result of drought-related displacement (including Lake Cahuilla's cycles) by the 1500s. So that's an automatic potential right there, although unless you can have such a spread on an earlier Lake Cahuilla cycle, it's more relevant to the New World in isolation, where the Old World never contacts them (or by ASB doesn't exist).
Any source on California arsenic copper ore? AFAIK most of the copper is in north eastern California and there were a few tin mines in LA and Riverside. Best place for a bronze age civilization in the US would be the Southwest. Arizona has the bulk of US copper deposits, with major mines near Tuscon. Meanwhile the only major American tin mine outside Alaska is at El Paso.
Continuing my previous response, arsenopyrite is very common in the PNW and California/Nevada and is blended in with copper sources there,
especially in mines along the California/Nevada border (hence why it would be very interesting to see the Washoe or Paiute gaining dominance based on their metallurgical skills/trade in copper/tin/arsenical bronze. But what this means is that theoretically, there's a lot of places which could make arsenical bronze, although likely Northern California will be the main origin of them since in most of the PNW the arsenic content would be too low.
Native copper might be the bottleneck. It's most noted amongst American Indians for use amongst some Dene groups (Ahtna of Alaska and some NWT Dene called the Yellowknives), the Copper Inuit (NWT), and the Old Copper Culture (Michigan), but I'm unsure how much native copper was laying around in the California/Nevada area. Manipulation of native copper is usually cited as a prerequisite for smelting copper. Could be that you'd need one of those Dene groups to develop copper smelting to get the ball rolling on things, and preferably pretty early since Dene peoples migrated quite a bit OTL (like the Pacific Coast Athabaskans of Oregon/California).
This really needs to be a proper TL...
I'll get there sooner or later in my own TL (sure it's an imported development, but no one ever slights the Mississippians or Europeans for importing agriculture). But I'd love to see an indigenous Californian TL here, since there's a lot of potential (epic earthworks/waterworks, orchards of domesticated oaks, the sky's the limit), you just need to work around the inherent issues regarding droughts and flooding. And from what I've found, it's surprisingly easy to find good public domain/free sources about California Indians compared to many other American Indian groups. There's quite a few solid (and relatively recent, no older than the 50s/60s unlike other free sources, so it isn't just classic works by Franz Boas and such) ethnographic/linguistic works, including dictionaries floating around out there.
I imagine along the coasts, considering the importance of seaweed and the kelp forests as well as shellfish to the indigenous people IOTL, that mariculture for kelp and shellfish could be of hugeeeee importance.
Also makes good fertiliser, as the Irish will attest to. I like the Chumash especially since they were great sailors and could serve as a nice link to Mesoamerica and the PNW.
interesting information, chia seeds were extensively used throughout California, and a different species of chia was a major source of calories for Mesoamericans. Similar to there being several species of wild amaranth, and domesticated varieties being incredibly important food crops.
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Source on this? Any discussion/maps there of other California Indian plants?