Talley Road is an easy, gently-sloping dirt road from River Road East
to the primitive Talley campground on the Rio Grande. Like most of the other dirt roads in the park, you wouldn't ride this trail for its technical merit or fun factor, but this is a far better way to see the park than from the window of your car.
Talley Road starts at the Mariscal Mine which is an interesting historical site worth a short visit. Keep in mind this was a cinnabar mine. Cinnabar is a toxic ore of HgS (mercury sulfide), and mercury is also extremely toxic, so take appropriate care.
Along this road, you'll have views of the Chisos Mountains to the northeast and the Mariscal Mountains to the east in a part of Big Bend National Park that few people visit. The road ends at the Rio Grande where you may enjoy a swim or some wading if the current is not too great. Don't cross into Mexico though; there is a $5000 fine to come back if you're caught.
Talley Road and the access from River Road East
are accessible by 4×4 high clearance vehicles (check with the park service for current conditions - 4×4 may not be required if they've recently graded the roads). The section between the Mariscal Mine and the intersection with Black Gap Road
was sandy when I rode it.
Keep in mind this is a desert and it can be very hot most months of the year. There is no potable water available along the route, so you'll want to carry more than you think you might need and there is no shade available. Winter is a great time for this ride, but the desert can get surprisingly cold in the winter, and the sun can still be intense. If you're unsure of conditions, check with a ranger.