Photos: Southwest canyon wonders

This mesa in Zion National Park, made of Najavo sandstone, has two sets of lines in it. The horizontal lines are frequently known as "crossbedding," and are representative of wind-blown sand that has developed into sand dunes, according to the National Park Service. The dunes became buried, and the grains of sand became glued together due to iron oxide and calcite, forming the sandstone. The vertical lines, meanwhile, are shallow cracks caused by erosion and stress on the surface of the rock. Causes included drastic temperature changes, expansion and contraction, and getting wet and then drying.