Differential weathering

Harder calcite (I think) veins weathering out of Aztec Sandstone. Valley of Fire State Park, Nevada, USA. The Aztec is correlative with the Navajo Sandstone of Utah and northern Arizona, but for historical reasons has a different name here. The calcite crystallized in cracks. You can tell this is a desert area, because the _calcite_ would weather first if the climate weren't so arid!