Chapter V—The Cenozoic Era 29

Bryce Canyon Formation 30 A Great Erosion Surface 32 Crustal Movement at Grand Canyon 33 Cutting the Grand Canyon 34 The Forming of Zion Canyon 37 Glaciers 38 San Francisco Mountain Volcanic Field 39 Elephants and Camels 41 Advent of Man in the Southwest 42 Bibliography 45

ILLUSTRATIONS

PAGE The Grand Canyon Frontispiece Diagrammatic Sections of Grand Canyon Region x Rocks of First Era, Inner Gorge of Grand Canyon 1 Block Diagrams of Events of First Era 3 Tilted Rocks of the Second Era, Grand Canyon 5 Diagrammatic Section of Third Era Formations, Grand Canyon 8 Scene on Cambrian Sea Floor in Grand Canyon Region 10 Trilobites Preserved in Green Shale of Grand Canyon Walls 11 A Fresh-water Fish of Devonian Age (Sketch) 12 Sea Life from the Redwall, Grand Canyon (Sketches) 12 Havasu Falls in Redwall Limestone, Grand Canyon 13 Tracks of Short-legged, Prehistoric Animal, Supai Formation, Grand Canyon 14 Landscape at Time Hermit Shale was Forming 15 Fossil Fern From the Hermit Shale, Grand Canyon 15 Wind-blown Sand, Coconino Formation, Grand Canyon 17 Tracks of Primitive Four-footed Animals, Coconino Sandstone, Grand Canyon 17 Marine Life From the Kaibab Limestone, Grand Canyon (Sketches) 18, 19 Diagrammatic Section of Fourth Era Formations, Southern Utah and Painted Desert Regions 20 Cedar Mountain 22 Red Butte 22 Petrified Forest, Arizona 23 Petrified Logs of Triassic Age 23 Dinosaur Tracks, Painted Desert 24 The Painted Desert 25 Zion Canyon, Navajo Sandstone 26 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.

From the rim of Grand Canyon one not only looks down through tremendous space, but also through time, glimpsing the record of vast ages, measurable not in centuries but in millions and even hundreds of millions of years. There in the bottom of that mighty chasm are found rocks formed during the first and oldest era—rocks in which the original structure has been entirely modified by great heat and pressure and in which no evidence of life has been found. There in the Grand Canyon are also seen two other great series of rocks, those of the second era which are partially altered and which contain earliest traces of plants, and those of the succeeding era in which are preserved primitive animals of many types.

Rocks of the fourth great era—the age of dinosaurs—lend color to the Painted Desert, and to the sheer walls of Zion Canyon. Beautiful little Bryce Canyon to the north boasts of some of the most recently formed rocks in the region—those of the fifth and last era, the age of mammals. The great volcanic mountains and the marvelous features of erosion, such as the canyons and the desert cliffs, are also developments of this most recent chapter. In brief, the Grand Canyon region affords some wonderfully interesting glimpses of ancient landscapes during many different parts of the earth’s history, and these make the past a moving, living thing.