Rainbow Natural Bridge, Navajo Sandstone 26 Cretaceous Shells From Southern Utah (Sketches) 27 Coal Canyon, Painted Desert Country 28 Bryce Canyon 30 Map of Colorado River 31 A Great Erosion Surface 32 Diagrammatic Cross Sections of Grand Canyon 35 The Grand Canyon 36 Zion Canyon 37 Chart of San Francisco Mountains 39 San Francisco Mountain—Past and Present (Sketch) 40 Map of San Francisco Mountain Volcanic Field 40 San Francisco Mountain 41 Elephant and Camel Remains 42 Ancient Indian Petroglyphs, Head of Bright Angel Trail, Grand Canyon 43 INTRODUCTION Probably no place in the world of similar area has recorded a more complete or a more interesting resume of the earth’s history than has the high plateau country of northern Arizona and southern Utah. Although many great events and some long intervals of time are not represented by the formations of this region, yet of the five major chapters or eras into which all of time has been divided by geologists, at least some parts of each have left their traces in this area. Whether on the brink of the mighty Grand Canyon, among beautiful logs of the Petrified Forest, or beneath the lofty walls of Zion—the “Rainbow of the Desert”—one looks upon rocks which are not alone curious or colorful, but which are also records of the past inscribed and illustrated in an intensely interesting manner. In one place is seen the sand of ancient dunes, in another the border of an early sea, or perhaps the floodplain of mighty rivers, and in all of these remain the unmistakable evidences of life—plants and animals preserved to make a reality of the living, moving past. Everywhere are found the evidences of those great processes of nature—erosion of the high country, land formation in the low country, and mighty crustal movements slowly raising or lowering the land in both.