By no means have I ever seen them before, but according to AntWeb, the most hardcore and elusive ants to find in NoCal would be Neivamyrmex sp. and Stigmatomma pallipes. Total S Class in my opinion, since they're very unique compared to other ants in the region. Polyergus and Strumigenys are also pretty cool. I just based these off on how awesome they look, their lifestyle, and their rarity
Gotta admit that Neivamyrmex are not hard to find if you know where to look.