There is a very noticable border checkpoint almost in between San Diego and L.A. - I believe all trucks and buses must pull in there for inspection, and they can pull cars in there randomly as well.

It is a full Customs search, although the majority of searchees never crossed the border or got closer to it than downtown San Diego.

The virtual border concept also extends to law enforcement - I believe there are rulings that permit warrantless/permissionless searches of cars, trucks and buses along certain stretches of interstate highway, like I-10 between Houston and Florida.

The judges that made this type of government action legal should be stripped of their citizenship and deported to North Korea to shine the Dear Leader's shoes.