Hiking down into the canyon is no joke. Black Canyon hikers need to start early, and be incredibly cautious as the trails have steep vertical drops and a lot of loose rock. I did the S.O.B. hike last summer on the North Rim (a wilderness permit was required) at Black Canyon, and despite our early start and decent pace, by the time we got down to the bottom of the canyon (and it set in that we had to hike back UP the 1800 vertical feet in 1.75 miles we just came down), the sun had made its way to the rim we had to hike back up, and it was unbelievably hot. If the Gunnison Route that this woman was on was similar to the S.O.B. (and from the Black Canyon website, it looks like it is), there truly is no flat place to stand during the entire hike (you stop hiking, you're holding on to something to keep you up)...which explains why her sons may not have been able to help as quickly as they could have otherwise. Very, very sad.