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:
The layers from the Esplanade Sandstone to the Watahomigi Formation are known collectively as the Supai Group. This illustrates the geological use of heirarchical terms for geologically similar layers, which we will encounter in lunar and planetary geology.
The Tapeats is the lowest layer dated before the beginning of the Cambrian period. Below it, and tilted are the Dox Formation, and several layers known collectively as the Unkar Group (see the next illustration). The lowest of these is the Bass Formation, dating from about one billion years ago. Still lower, dating from 1.5 billion years or a little more is the Vishnu Group, including the Vishnu Schist.