Evolution of the Landscape of the San Francisco Bay Region

By Arthur D. Howard

This title is part of UC Press's Voices Revived program, which commemorates University of California Press’s mission to seek out and cultivate the brightest minds and give them voice, reach, and impact. Drawing on a backlist dating to 1893, Voices Revived makes high-quality, peer-reviewed scholarship accessible once again using print-on-demand technology. This title was originally published in 1962.
This title is part of UC Press's Voices Revived program, which commemorates University of California Press’s mission to seek out and cultivate the brightest minds and give them voice, reach, and impact. Drawing on a backlist dating to 1893, Voices Revived

• Language: English
• Publisher: University of California Press
• Release date: Mar 29, 2024
• ISBN: 9780520315235

Arthur D. Howard

Enter the Author Bio(s) here.

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California Natural History Guides: 7

EVOLUTION OF THE

LANDSCAPE

OF THE

SAN FRANCISCO BAY REGION

BY

ARTHUR DAVID HOWARD

UNIVERSITY OF CALIFORNIA PRESS

BERKELEY, LOS ANGELES, LONDON

UNIVERSITY OF CALIFORNIA PRESS

BERKELEY AND LOS ANGELES, CALIFORNIA

UNIVERSITY OF CALIFORNIA PRESS LTD.

LONDON, ENGLAND

© 1962 BY THE REGENTS OF THE UNIVERSITY OF CALIFORNIA

FOURTH PRINTING, 1974

ISBN: 0-520-00577-5

LIBRARY OF CONGRESS CATALOG CARD NUMBER: 62-17535

PRINTED IN THE UNITED STATES OF AMERICA

CONTENTS 1

CONTENTS 1

INTRODUCTION

THE MODERN LANDSCAPE

THE REGIONAL SETTING

THE LOCAL SETTING

PROBING THE PAST

THE PROBLEM OF THE BEGINNING

THE GREAT INUNDATION: THE MIOCENE EPOCH

END-MIOCENE MOUNTAIN-MAKING

THE LESSER INUNDATION: THE PLIOCENE EPOCH

LATE-PLIOCENE MOUNTAIN-MAKING

THE GREAT DENUDATION

THE PLEISTOCENE EPOCH

THE FIRST STAGE

THE SECOND STAGE

GENERAL REFERENCES

INTRODUCTION

The majestic setting of the San Francisco Bay Region, with its picturesque land-locked harbor, its rugged mountain border, and its lovely valleys, represents the culmination of a remarkable series of natural events that had its beginning many millions of years ago. Few realize that on a number of different occasions within the recent geologic past, mountains were upheaved here only to be later worn to their roots; that the waters of the Pacific repeatedly flooded the area even to the site of the present Sierra; that generations of volcanoes came into existence, spread lava and ash over the landscape, and then disappeared; that titanic forces cracked the surface of the Earth and jostled great blocks about like cordwood; that the climate at times was far less pleasant than now, sometimes much warmer, sometimes much colder.

The landscape is not immobile, nor permanently set in stone. On the contrary, it is continually changing. Its appearance at any one time represents a fleeting episode in an endless struggle—a struggle in which powerful forces from within the Earth are arrayed against forces from without. The internal forces crumple and break the outer shell of the Earth and heave it into mountains. Their activity is generally accompanied by volcanic activity and jarring earthquakes. We must not suppose, however, that the rise of mountains is cataclysmic; from the human standpoint it is painfully slow. It is true that in some regions, like the western United States, an entire mountain range may break loose from its surroundings and snap upward a few feet, but these movements rarely occur more than once a century. Thus, the average rate of growth of such mountains is only a few inches a year. Other ranges rise without perceptible movement, by an infinitesimally slow buckling of the ground. Precise surveys , however, when periodically repeated over long spans of time, reveal these faint changes in elevation. The cumulative effects of even these imperceptible movements are the lofty mountains of the Earth. This explains why we find entombed in the rocks of many high peaks the fossilized shells of creatures that once lived in the sea, thousands of feet below.

Against the powerful internal forces are arrayed others, much less spectacular, that operate more subtly and insidiously and pass largely unnoticed. These are the forces of weathering and erosion which slowly but relentlessly nibble away at the highlands created by the forces from within. When the internal forces dominate, mountains stand high and dot the surface of the Earth; when the internal forces are dormant, the processes of weathering and erosion dominate and carry the substance of the mountains into the sea. There have been times in the past when the internal forces lay dormant for such long periods of time that the mountains in some regions were completely obliterated and the landscape was reduced to a low plain.

The landscape, then, changes constantly at the whim of the forces that produce it. The present landscape

THE MODERN LANDSCAPE

The over-all landscape of middle California, from the latitude of Cape Mendocino in the north to the Tehachapi Mountains in the south, is relatively simple. It consists of three major topographic units: the Sierra Nevada, the Great Valley of California, and the Coast Ranges.

THE REGIONAL SETTING

The Sierra Nevada, one of the world’s great mountain ranges, forms a 400-mile-long barrier between the arid lands of Nevada and the Great Valley of California. Trap-door-like in profile, the range presents a precipitous escarpment on the east—a rugged wall that must have dismayed the early pioneers seeking to reach the California gold fields. The crest of the escarpment is topped by a line of lofty peaks of which Mt. Whitney, the highest peak in the United States exclusive of Alaska, is perhaps the best known. The descent from the High Sierra westward to the Great