Slot canyons

From the Madame Scherzo blog:

Slot Canyons of the American Southwest

Few places on Earth have such beauty and mystique on an intimate scale as the delicately sculptured and colored slot canyons of the American Southwest. There are thousands of scenic canyons in this region but most are relatively wide; in contrast, slot canyons have vertical walls and may be hundreds of feet deep but only a few feet wide.

The general rock is sandstone, in various shades of red and orange; it is sunlight, shining down and reflecting along the canyon walls that gives the canyons their special beauty; the shadows and colors change constantly as the sun moves overhead.