Traveling between states in the US should never be restricted unless there is reasonable suspicion that a crime is being committed.
Where is the warrant, Janet Napolitano?
Unless they are illegal aliens who are potential Democratic Party voter. Then they can come ad go as they please.
Did you give a second to wonder why there is an inspection post at the border?
Much of the food grown in the United States is grown in California. Protecting that food supply from pest is necessary.