I travel weekly from PHX to So Cal. In the last year, there has twice been a border patrol stop on I-10 just west of the rest stop which would be right around mile marker 4. Both times there was not a stop on Eastbound I-10. Next time you pass the rest area just before the AZ – CA state line – look to the right and you will see a small building on a small off ramp. That is where they set ip their operations at. The first time there were dogs, the second there was not.