We've been to San Mateo around 20 or more times and have not been hit with ants. But, it can happen anywhere. I the old days, people would sprinkle Ajax (the white powder) around the tires, jacks, etc, but that has been banned at San Mateo and all state campgrounds as it's considered toxic. There are powders you can use like borax, talc, etc that some folks use.
BTW, we just got hit with ants up at Lake Casitas, about 200 miles north of San Mateo. First time in 9 years we had a ant problem and it was no fun. They came down of the roof of the trailer via a tree. Got rid of most of them with ant spray outside but brought a few home too!