They've been doing that shit for years, they case NV gun shows and make lists of CA plates and transmit it to CHP waiting on the CA side on the two or three typical highways that go into CA. I think the NV gun show promoters figure by coddling the communists they won't get sued or whatever, who knows.
It would be funny as hell to troll the shit out of them though, like buy a bunch of pmags, stop 50 (or so) yards short of the border and start juggling pmags while another guy comes out with an air horn and honks it at random odd intervals. And then wait until random pickup trucks drive by and throw a pmag into the back of them or something like that... then get back in your car and drive further back into nevada.
ETA: Even Better- Buy like a case of pmags, put them into your CA plated car. Before hitting the border, hand off the cases of mags to someone going the other
direction. Then when you get pulled over by CHP you can be like "this is going to be fun in court".
-Mike