

US states don’t have inter-state border controls beyond some weight checking for semis
California does have agricultural border checkpoints, though that doesn’t really change things from the topic of whether population movement could be viably limited.
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https://www.cdfa.ca.gov/plant/PE/ExteriorExclusion/borders.html
Apparently the term is “California Border Protection Stations (BPS)”.












Not quite what you’re asking, but up until about the 1870s, the US had effectively unrestricted immigration.
Some economist at the Cato Institute, Alex Newrath or something like that, did some interview with NPR Planet Money a few years back and estimated what potential immigration would be if restrictions were dropped.
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Alex Nowrasteh.
https://www.npr.org/transcripts/172501563