How did indigenous Mexicans get from the Siberian land bridge to Mexico without passing through California?
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They had Transporters or else they had some other form of magic. This is well documented by the various theories promulgated by science today.
Alternately, they took boats down the coast, skipping over the rich land and fishing resources, in a mad dash to become the first Mexicans.
Oddly enough the rich resources of California never bred any highly civilized peoples. When the Spanish came they found quite primitive hunter-gatherer clans. Unlike the Misissippi and Ohio river cultures. Or even the agricultural Iroquois or Algonquins.