I just want to echo that I agree strongly with Dave that no matter what the issue or how controversial it is you can't be afraid of discussing it openly and frankly. I know there are people right now reading this thread thinking it's awful that this is even being discussed - but frankly I say they're the kind of people who cause more problems than they can ever admit just by keeping their heads in the sand.
I also want to clarify that what I said above was not specific to the dunes or OHVers but rather my feelings in general about the issue of drug use in general. It goes the same for hikers as it does for OHVers whether they be in a national forrest, in the dunes, in the middle of the Mojave, or floating on a boat in some lake.
As for the border. Well frankly it's no marked at all. There are little stone blocks about 1 foot square every 1,000 feet (I think - it could be quite a bit more.) and then slightly larger markers every 5th one or something and then really big obelisk markers every 10th. My numbers are probably way off but that's the basic idea.
One of the big markers is really easy to find at Buttercup. Just go to the extreme western edge of the dunes where the midway campground is. Then go south until you hit the border. Even though the border isn't marked it is fairly easy to recognize in this particular area because it's hard pack and the BP drags it with tires on a regular basis to make it smooth so they can see any crossing. Then follow the path along the border east and just as you reach the dunes you'll find one of the big obelisks.
Here's a page about them:
http://www.ranchrescuecolorado.com/Border%20Monuments.htmHere's a shot of one of the smaller ones:
http://www.virtual29.com/hummers/SArizona/...20monument..htmHere is another site with shots of similar markers:
http://www.oz.net/~geoffsi/sw2001-web/index-808.htmBut overall the border is unfenced and unmarked but HEAVILY watched. The BP has cameras, VERY sensitive siesmographs (that can pick up footfalls), radar, night vision and other goodies they use to watch this area. I had neighbors who were BP stationed in the dunes and I know from talking to them that the number of BP in that immediate area at any given time is MUCH higher than it appears.
BTW - the BP really dosn't have any issues with people crossing over into Mexico. The Mexican Federales are the ones to worry about upsetting by doing that - but they pretty much stay out of the dunes and don't pay attention. The problem is when you try to come back in. If you don't cross over at a recognized point of entry then you're illegally reentering your own country and can end up in a heap of trouble. I've been let off with a warning a few times when I accidentally strayed too far south (but always returned as soon as I realized it.) but I've talked to people who had their quads and buggies confiscated and had to pay though the nose in fines and fees to get them back. The nearest point of entry is Andrade at Algodones a few miles east of the dunes.