Exposure can be a problem for photographers in these deep and dark canyons. The low light levels require a tripod and long exposures on slower speed, fine-grained films. Fast films are too grainy and electronic flash is too harsh and the color of the light from an electronic flash is too blue. Exposure times may be anywhere from several seconds to many minutes long. Small apertures and low light levels mean long exposures.
Contrast can be a problem.
Bright highlights illuminated by direct sunlight on canyon walls should be avoided. Color slide films cannot record the great range of light found in these canyons. I always base my exposure calculations on the brightest reflected highlight, not direct sunlight on the walls. With a one-degree spot meter, I measure the brightest highlight in my framed composition that has visible detail that I want to appear on my film. I take that one-degree spot meter reading and increase it by two stops.