Some fire killed off most of the cottonwoods in the area.  Too bad since they are wonderful shade trees and I enjoy hearing the rustle of leaves at night.  It could have been a lightening strike since lightening does go down into the canyons but it could also have been careless campers with a campfire of which there are numerous marks.  I am not a friend of campfires, they unnecessarily disturb the undergrowth and degrade the living habitat of creatures and plants in the area.  If your really want a campfire then take along a fire log (about $1.80-$2.50) and cut it into smaller pieces.  I've done that and gotten over an hour out of a third of a log.  

Please be certain that your campfires are 100% out.