This was a day trip in February 2006 and was an interesting experience. I lived in Orange County for a couple of years and San Diego is about an hour south so not too far. My bike at the time was a 2003 Suzuki V-Strom DL1000. Quite heavy but it did allright on the rocky and sandy roads in this border area. As I am not an experienced dirt rider, the ride went at slow speeds as crashing in the middle of nowhere isn’t a good thing.
I went off the main road not too far east of San Diego / Tijuana and found a dirt road that looked interesting. After riding for a while, I noticed quite a few white/green border patrol vehicles you often see in this area. So that was a good indication I wasn’t too far from the border.
The dirt road went close along the border fence in some places. In other places, there was no fence but you could still tell where the border was. Often, the road seemed deserted but you can sometimes spot the occasional border patrol truck hiding around a corner. At other times, when you think you’re alone, suddenly a border patrol vehicle shows up in your rear-view mirror.
They never stopped me so it seemed ok to be riding there. A friendly wave often is a good way to show you have no bad intentions. At one point, the border fence was just a row of poles and there was nothing stopping me from riding across. Probably not a legal border crossing.. The area appeared generally safe but I guess you just never know what you can encounter.