Complex sentence: Two types of stone were procured from the sandstone cliffs that form Chaco Canyon; a hard gray-brown tabular sandstone that forms the bench above the canyon cliffs, and a softer, tan, massively bedded sandstone that forms the cliffs themselves.
Split into simpler sentences: Two types of stone were procured from the sandstone cliffs that form Chaco Canyon. A hard gray-brown tabular sandstone that forms the bench above the canyon cliffs, and a softer, tan, massively bedded sandstone that forms the cliffs themselves.