Saturday, December 23, 2006
Checkerboard Mesa, Zion National Park, Utah
This is what the sign told me about the cracks in the rock:
"The horizontal lines, commonly called crossbedding, represent layers of wind-blown sand that built up into sand dunes. These dunes were then buried, and the sand grains glued together by calcite and iron oxide to form sandstone. . . . The vertical lines are less common. They are actually shallow cracks that result from stress and erosion on the rock surface. These cracks are probably caused by expansion and contraction, temperature changes, wetting/drying, or a combination of these processes.