First, I loved using Kodachrome, 25, 64, and 125; those were the days. When Kodak discontinued Kodachrome, I began using Fuji 50 and 100 for transparencies. I did primarily editorial work on an assignment basis. The editors or art directors accepted Fuji as a replacement for Kodachrome. I was also represented by a stock agency, which I supplied from my own stock files.
I have been to Big Bend twice, both times in late fall, never in the summer. Be aware that hiking conditions vary from flat to steep. Water, water. People try to hike Big Bend in summer, without sufficient water or clothing with very adverse results.