During the early period of the Miocene, that country which lay between the Rockies and the Pacific was a flat plain of low relief, with meandering streams and vague divides. Occasional rounded hills broke the monotony of this plain. These were but the abraded stumps of a pre-existing mountain mass—the ruins of mountains that had been. About _Jurassic_ time a general disturbance occurred in the present region of the Sierra Nevada. This was accompanied by an intrusion of a vast body of molten rock which, when solidified, became the granite of the Sierra. During the _Cretaceous_ the entire region between the Rockies and the Pacific again awoke and began to bulge at slow and intermittent intervals. The Sierra block had its origin during one of these upheavals and acquired a slight westward slant. During the age that gave man to the world, the Sierra was uplifted to the light. About the dawn of the _Quaternary_, the last of the great divisions of geological time, the greatest manifestation of Sierra mountain building took place. This convulsion of the earth hoisted the snowy range to its present sublime elevation. Following this upheaval came an age of ice. It is to this period that Yosemite Valley owes its glaciation. In fact, the present indefinable charm and fierce grandeur of the High Sierra are legacies of this reign of ice. However, the glaciation of the Sierra must not be correlated with the continental glaciations which ushered in the age succeeding the Miocene. The former glaciation is “more properly to be regarded as corresponding to the very last episode of that long and varied chapter in the geological history of the continent,” states Lawson. Though the final uplift of the Sierra block is a long time past as years go, geologically speaking it is not remote. Indeed, the Sierra Nevada might “safely be placed among the young and giddy mountains of our planet.” From the comparative point of view, on the other hand, the waste of years that have elapsed since the Sequoia first waved its magnificent evergreen dome toward the heavens is bewildering. Impressive as the evolution of the Sierra must have been, few of the dramas of the earth which science has restored are more wonderful than the restriction of the Sequoia exclusively to the mountains of California. The record of the rocks following the great Age of Reptiles tells quite a different story. With amazing abruptness all the rich diversity of reptilian life apparently ceased. Some change seems to have occurred, blotting it out forever, for not a scrap of evidence remains of its continued existence. The _dinosaurs_ are no more; the _pterodactyls_ have vanished. A new type of life, that of the mammal, now holds dominion over the earth. Most astounding of all, the Sequoia still carries on, even to the present day—living survivor of the Age of Reptiles.