Checkerboard Mesa. This striking outcrop of rock is unique to the Zion National Park, Utah, USA. The rocks are fossil dunes that show the cross bedding characteristic of the aeolian (windblown) sandstones of the Navajo formation, which were deposited during the Jurassic period (around 200 to 145 million years ago). Over time these massive sandstones have been affected by the combined action of faulting, which broke the formation up into large blocks, and weathering, which subsequently accentuated the outlines. This type of weathering, known as spheroical, is a consequence of the combined action of rain, snow and frost.