Im drawn to the seemingly endless back roads down here. Even with a high clearance 4WD vehicle if the road says its washed out you better believe it (or you might just travel 25 miles only to have to turn around and go back).
Without an off-road machine down here youre going to be pretty limited. The road to the mercury mine was out last time I was there and so was part of the river road. And sometimes a road isnt closed but its still impassable.
We like to go in the off season (less tourists) but it can get hotter than Hell. There 2 or 3 types of rattlesnakes, a couple different scorpions and a host of plants with giant thorns to shred all you "short pants hikers" up. And theres no water to speak of just wading in the Rio Grnade here is not advisable let alone drinking from it. Mexican towns allow untreated sewage to run off into the river as well as who knows what industrial waste gets dumped in here.
Do not cross the river either. Sure theres a hundred miles where nobody will see you but if they do your ass is in really big trouble. Mexico has no problem letting their citizens come across but if you do and they catch you it will cost you plenty. Even our own Border Patrol will hassle you if they think you were crossing over.
Anyway take two spare tires, extra water and a flashlight. Fill up with gas in Terlingua before you enter either the SP or the NP. There is no cell phone service over most of this area.