I passed two of them, had to stop at one.
The first was on CA 111 on Sept. 25th. We were going south on 111 and didn't have to stop, they were only checking the northbound. The post is south of Bombay Beach, north of Niland.
The second was on CA 78. CA 78 goes east out of Brawley, then swings northeast.up to Blythe. We had to stop at this one, Sept. 26th, and they just waved us through. It is located east of the Imperial Sand Dunes between Glamis and Blythe. We were worried about this one. All these checkpoints have dogs. I was with my wife and two cats in a small van with our road supplies; a pretty full vehicle. We were worried they would tear the van apart looking for whatever, make a mess and terrify our cats. I was relieved when they ignored us. However, they can and will check out anyone they want for illegals and drugs, as Matt said.
On a side note, we didn't see or feel any earthquake activity on the two days we were down there.