The "Coast Range Revolution" took place in the midst of the Tertiary period. Over the site of the Coast Ranges, strata had accumulated, especially during Cretaceous and earlier Tertiary times, to a thickness of thousands of feet. In middle Tertiary time these strata were subjected to a mountain-making force of compression and more or less folded, faulted (fractured), and uplifted into the Coast Range Mountains. Some portions of the range were intensely folded and faulted and upraised many thousands of feet, while other portions were only moderately folded and uplifted. It is an interesting fact that the great San Francisco earthquake rift or fault originated at this time. It was a renewed, sudden movement of a few feet along this fault which caused the disastrous earthquake of 1906. Still other considerable earth movements took place in the Coast Range region during late Tertiary and Quaternary times, as, for example, uplift without folding, as proved by distinct sea-cut terraces at altitudes of more than a thousand feet, like those north of San Francisco and south of Los Angeles. A moderate amount of still later subsidence has caused the development of San Francisco Bay. The large islands off the coast of southern California have in very recent geologic time (probably Quaternary) been cut off from the mainland by sinking of the land. [Illustration: Plate 11.--(_a_) Part of the Mammoth Hot Springs Terrace in the Yellowstone Park. The view shows the deposit with boiling water flowing over it. The water enters the earth back on the mountain, travels underground in contact with hot lava, rises through limestone, from which the boiling water takes into solution much carbonate of lime which is deposited when the water reaches the surface. (_Photo by Jackson, U. S. Geological Survey._)] [Illustration: Plate 11.--(_b_) View Across Part of Crater Lake, Oregon. This great hole, 3,000 to 4,000 feet deep and 6 miles in diameter and now partly filled with a lake 2,000 feet deep, was formed by a subsidence of the top of a once great cone-shaped volcano fully 14,000 feet high above the sea. The high rock in the distance rises 2,000 feet above the lake which is over 6,000 feet above sea level. The island is a small volcano of recent origin. (_Photo by Russell, U. S. Geological Survey._)] [Illustration: Plate 12.--(_a_) Detailed View of Part of the Very Oldest Known (Archeozoic) Rock Formation of the Earth. The rock is distinctly stratified and represents sands and muds deposited layer upon layer upon a sea floor at least 50,000,000 years ago. The sands and muds first consolidated into sandstone and shale below the earth's surface. Then, under conditions of heat, moisture, and pressure, they were notably altered, mainly by crystallization of minerals, and raised high above sea level. Finally the strata were laid bare by erosion. (_Photo by the author._)]