With the close of the age of fire, the mountain chains were in place, as they now stand, but the plains and valleys were not yet fashioned. Another series of forces must needs come to elaborate the rude outlines of the land. And so came on the third great age, the age of flood. The upheaval of the mingled granite and volcanic masses of the Cascade and Blue Mountains, while at the same time the Rockies were undergoing the same process, imprisoned a vast sea over the region now known by Westerners as the Inland Empire. In the depths of this sea the sediment from a thousand torrents was deposited to fashion the smooth and level valleys of the Yakima, the Walla Walla, the Spokane, and lesser streams, while a similar process fashioned the valleys of the Willamette and other streams between the Cascades and the Coast Mountains westward. But while the age of flood was shaping the great valley systems, a fourth age--the age of ice--was working still other changes upon the plastic land. The mountains had been reared by upheaval and volcanic outflow to a stupendous height. Then they became glaciated. The whole Northern Hemisphere, in fact, took on the character of the present Greenland. Enormous glaciers descended the flanks of the mountains, gouging and ploughing out the abysmal canyons which now awe the beholder, and scooping out the deeps where Chelan, Coeur d'Alene, Pend Oreille, Kaniksu, and other great lakes delight the vision of the present day. Such were the forces that wrought the physical features of the land where the River flows. We do not mean to convey the impression that there was a single age of each, and that they followed each other in regular chronological order. As a matter of fact there were several eras of each, interlocked with each other: upheaval, fire, flood, and frost. But as the resultant of all, the Columbia Basin assumed its present form. The great forces which have thus fashioned this land manifested themselves on a scale of vast energy. Evidences of upheaval, fire, flood, and glacier are exhibited on every side, and these evidences constitute a testimony of geological history of the most interesting nature. Long before this record of the rocks had found a white reader, the native red man had read the open pages, and interpreted them in the light of his ardent fancy. The Indian conception of the flood, involving also that of the creation of the native tribes, is one of the most fantastic native legends. This is the story of the great beaver, Wishpoosh, of Lake Kichelos. According to this myth the beaver Wishpoosh inhabited that lake on the summit of the Cascade Mountains, the source of the Yakima River.