There are several phone apps that will tell you where the campgrounds are. Personally, I've never tried to camp where I'm not allowed (I don't count sleeping on a picnic table at a rest stop). One can often (usually?) find a campground either actually in town, or a few miles down the road. To my knowledge, I've never been turned away with a tent; there's always a 10x10' spot of grass to rent me.
Alternatively, if you're in a U. S. National Forest and can find a spot off the road, you can camp anywhere you want. It's how we do the majority of our camping in our VW Westfalia, where in Washington there are a plethora of spots 90 minutes from our house (no, I'm not telling <g>).
But that's for my mode of travel, which is usually off the beaten path. If you're looking for a place to stay in SF during WWDC, my advice will do you no good. OTOH, I rode to a conference in San Diego, had some room trouble and found a campground smack in the middle of SD a few miles from the hotel. So, I dunno, there might even be a campground in SOMA I don't know about. :-) (EDIT: curiosity got me: there's one out by Candlestick Recreation Area, if you don't mind paying $89/night!)
Alternatively, if you're in a U. S. National Forest and can find a spot off the road, you can camp anywhere you want. It's how we do the majority of our camping in our VW Westfalia, where in Washington there are a plethora of spots 90 minutes from our house (no, I'm not telling <g>).
But that's for my mode of travel, which is usually off the beaten path. If you're looking for a place to stay in SF during WWDC, my advice will do you no good. OTOH, I rode to a conference in San Diego, had some room trouble and found a campground smack in the middle of SD a few miles from the hotel. So, I dunno, there might even be a campground in SOMA I don't know about. :-) (EDIT: curiosity got me: there's one out by Candlestick Recreation Area, if you don't mind paying $89/night!)