That caliche is like concrete.
Nevada, Utah, Arizona, and parts of Colorado used to be under a giant pre-historic lake called Lake Lahontan. Coastline was the Sierra Nevs and the Rockies. When that thing dried up, it baked under the sun, and today you get caliche. Up around Ely and Caliente, they have dug up Ichthyosaurs.
http://www.ucmp.berkeley.edu/diapsids/ichthyosauria.html