It's a pavement-only ride and the roads are generally well maintained. Hwy 170 from Terlingua to Presidio is one of the top 5 motorcycling roads in Texas. From Presidio follow the signs to international bridge into Mexico. On the Mexican side of the bridge there is a checkpoint. Most times you get waved right through but every so often you will get directed to the side for a cursory search (they are looking for weapons, drugs, etc. - same stuff our customs guys look for when they stop you coming back into the USA). Once through the checkpoint it is a straight shot south through Ojinaga and on to Peguis. Navigationally, it is very easy because you are on the main road and don't have to turn off of it to get to Peguis.
There are no checkpoints between Ojinaga and Peguis. Just ride south till you get to the canyon.
Reverse your course to get back to the USA. After crossing the international bridge into the USA you will likely sit in a short line. Once you get to the head of the line the customs agents will stop you, ask you for your passport, and check your identity on their computer system. Most times they will let you through after inspecting your papers. Sometimes they will want to have a look in your bags (assuming you have a tank bag or other bags on your bike). At this point you will marvel at how easy it was to get into Mexico and how much longer it takes to get back into the USA.