This was a day we'd been building up to and slightly dreading. We'd be gaining ~2,100 feet by bike, stashing our bikes near the Homer Wilson Ranch trailhead, switching to backpacking mode, and gaining another ~3,000 on foot hiking up the Blue Creek Trail to the South Rim of the Chisos. (If you picture "Blue Creek" as something that contains water, you do not know Big Bend.)

The bike portion of the day was along Ross Maxwell scenic drive as it climbs from the Rio Grande into the foothills of the Chisos. The foothills are very geologically diverse with hills of compacted volcanic ash punctuated by jagged igneous dikes and all sorts of other stuff that's beyond my geology knowledge.