We took the petrified dunes and red sand trails in to the canyon, which is a fairly arduous and hot path but clearly marked and padre canyon is beautiful - well worth the trek in. There was no one around and we found many opportunities to scramble and climb the mountains to the left of the canyon. The actual trailhead is immediately to right (easy to walk past) but even if you miss the trail there's still plenty to explore. Make sure you bring lots of water - it gets very hot and once you get in you'll want to keep going.