The Coast Ranges also have had a complex history with many vicissitudes.  The earliest foldings of their strata belong to the close of the Jurassic, but it was not until the end of the Miocene that the line of mountainous islands and the heavy sediments which had been deposited on their submerged flanks were crushed into a continuous mountain chain.  Thick Pliocene beds upon their sides prove that they were depressed to near sea level during the later Tertiary.  At the close of the Pliocene the Coast Ranges rose along with the upheaval of the Sierra, and their gradual uplift has continued to the present time.

The numerous north-south ranges of the Great Basin and the Mount Saint Elias range of Alaska were also uptilted during the Tertiary.

During the Tertiary period many of the loftiest mountains of the earth—­the Alps, the Apennines, the Pyrenees, the Atlas, the Caucasus, and the Himalayas—­received the uplift to which they owe most of their colossal bulk and height, as portions of the Tertiary sea beds now found high upon their flanks attest.  In the Himalayas, Tertiary marine limestones occur sixteen thousand five hundred feet above sea level.

Volcanic activity in the tertiary.  The vast deformations of the Tertiary were accompanied on a corresponding scale by outpourings of lava, the outburst of volcanoes, and the intrusion of molten masses within the crust.  In the Sierra Nevadas the Miocene river gravels of the valleys of the western slope, with their placer deposits of gold, were buried beneath streams of lava and beds of tuff.  Volcanoes broke forth along the Rocky Mountains and on the plateaus of Utah, New Mexico, and Arizona.

Mount Shasta and the immense volcanic piles of the Cascades date from this period.  The mountain basin of the Yellowstone Park was filled to a depth of several thousand feet with tuffs and lavas, the oldest dating as far back as the beginning of the Tertiary.  Crandall volcano was reared in the Miocene and the latest eruptions of the Park are far more recent.

The Columbia and snake river lavas.  Still more important is the plateau of lava, more than two hundred thousand square miles in area, extending from the Yellowstone Park to the Cascade Mountains, which has been built from Miocene times to the present.

Over this plateau, which occupies large portions of Idaho, Washington, and Oregon, and extends into northern California and Nevada, the country rock is basaltic lava.  For thousands of square miles the surface is a lava plain which meets the boundary mountains as a lake or sea meets a rugged and deeply indented coast.  The floods of molten rock spread up the mountain valleys for a score of miles and more, the intervening spurs rising above the lava like long peninsulas, while here and there an isolated peak was left to tower above the inundation like an island off a submerged shore.