The scale on the left gives the altitude, running from sea level to a little over 8,000 feet at the surface. The different geological groups and formations will be listed below, since they are not easily read from these reproductions. These are listed with their ages in millions of years:
The oldest rocks of the Grand Canyon are the Vishnu Schist. The foliation of these rocks is indicated by the curved lines in the yellowish area toward the bottom of the diagram. These metamorphic rocks have were intruded by the Zoroaster Granite perhaps 1.5 to 1.6 billion years ago. The granite is indicated by dashes at random angles in a pinkish background.
Click here for a view from the Colorado river.