Little Yosemite Valley is essentially similar to the Greater Yosemite in features and also in the manner of creation. Its walls are from fifteen hundred to two thousand feet high, its length is about three miles, its width one half-mile. Its floor, like that of the Greater Yosemite, was for a time a lake. In origin and history, the Hetch-Hetchy Valley, too, is almost identical with the Yosemite. Nature often changes the scene, often puts on a new landscape. The forces of erosion are steadily at work; most of them work slowly, but sometimes a change is wrought suddenly. When the Sierra was first upheaved it was more or less tilted, terraced, and fissured. The surface was uneven. The present topography is the product of a long and complicated series of events. It has been wrought out by many erosive forces. It probably has been acted upon by two or more ice ages, but the last age shaped the splendid topography of the Yosemite that is attracting the world to the scene. The eroding power of ice is determined by its thickness, that is to say, by its weight. The small, shallow glaciers wear much more slowly than the deep ice-streams that bear heavily upon the surface passed over. The ancient glaciers of the region took on vast proportions. An enormous and deep ice-field accumulated from the snows of Mounts Dana, Lyell, Gibbs, McClure, Conness, and other peaks. Flowing westward, it came in contact with Mount Hoffman, against which it divided. The right section flowed down into the Tuolumne; the left, a branch about two miles wide, swept upward, climbing about five hundred feet over the pass and descending upon the Lake Tenaya region. Apparently, five glacier streams united in the Yosemite Valley. They not only filled it but deeply overflowed the highest points on its walls. Passing out of the lower end of the valley, the united glacier was forced to climb upward several hundred feet. About twenty-five small glaciers still remain in the Yosemite National Park. There are about two hundred and fifty glacier lakes, mostly small. Others have filled with sediment and are hidden and forgotten. Lake Tenaya, the Lake-of-the-Shining-Rocks, has a surrounding of dense rock-masses that still show the rounded form and the high polish given by the ice. 2. TREES AND FORESTS The tree growth and the forest arrangement in the Yosemite National Park are among the grandest of such features on the globe, and they form one of the chief attractions of this heroic realm. The trees grow to enormous size and are distributed and grouped with crags, meadows, terraces, cañons--all in unmatched wild, artistic charm and sublimity. Though some areas are covered with growths tall and dense, they are free from gloom, and everywhere one may walk freely through them. They are broken and brightened with numerous sunny openings. This splendid landscape gardening extends over the greater portion of the Park.