Not very many roads enter California, as it has natural geological borders. An ocean to the west, hilly forest to the north. On the east, a 3 km high mountain range which leads into a hot desert, cut by the mighty Colorado. The terrain is a lot more forgiving to the south, but there’s an artificial border with Baja California there.

Plus, most of the infrastructure is there for the agricultural inspection stations. Just use it to stop human disease instead of plant disease.

Logically that makes sense but we can't even seem to secure our southern border with Mexico.

And interestingly there are only 16 agricultural stations for all of California. They are only in place at major highways.

https://en.wikipedia.org/wiki/California_Border_Protection_S...

And if I kind of zoom into Google maps I count 36 crossing between the Oregon/California border just between the Pacific ocean and I-5. Sure, a lot of those are probably logging roads and such, but that's just a 60 mile stretch.

I mean it’s not like the inter state borders in Australia aren’t absolutely huge, too...

Maybe they could build a wall.