GRAND CANYON OF COLORADO RIVER. In crossing the high plateau region of southern Utah and northern Arizona, the Colorado River has cut the greatest canyon in the world. It is more than a mile deep in places and the deeper portion is about 200 miles long. It is not only the most notable scenic spectacle of its kind, but a remarkably dear and impressive exposition of geology, pre senting many features that can be readily under stood. The rocks are bare, and while most of them are in thick beds lying nearly level some are tilted at various angles. They represent a long portion of geologic time from the Archaean, or oldest known, to the late Carbon iferous, but deposits of Ordovician, Silurian and most of the Devonian ages are absent. These rocks constitute cliffs and buttes of great variety of form and much brilliancy of color, forming a most stupendous and beautiful specta cle. The features presented illustrate most clearly the titanic process of nature's sculptur ing, not only in the present configuration but in the former land surfaces of earlier geologic times.
The term Grand Canyon is applied to that portion of the canyon of the Colorado River which lies in northern Arizona. It is in the midst of a wilderness and inaccessible from most directions, but -the Atchison, Topeka and Santa Fe Railroad has a branch line to its southern rim at a locality where some of the finest features are visible. Here are hotels from which trips can be made along the rim and down trails to the river's edge. Some views in this vicinity are given in the plates herewith. The altitude here is 6,866 feet above at the river just north it is 2,355 feet ; on the farther rim to the north it is 8,000 feet.
Few persons can realize on first view that the canyon is nearly a mile deep and from 8 to 10 miles wide. The cliffs descending from the rim form a succession of huge steps, each 300 to 500 feet high, with steep rocky slopes between. These cliffs are the edges of hard beds of lime stone or sandstone, while the intervening slopes mark the outcrops of softer shales. These beds
are more than 3,500 feet thick and they lie nearly horizontal. Far down in the canyon is a broad shelf caused by a basal hard sandstone; it is deeply trenched by the narrow inner canyon cut a thousand feet or more into the underlying Archaean The rocks of the canyon walls vary in color from white and buff fo bright red and dull green. They present a marvelous variety of picturesque forms fashioned mainly from ero sion by running water, the agent wlaich has ex cavated the canyon.
The Colorado River, one of the largest in North America, rises in the Rocky Mountains in Colorado and Wyoming and empties into the Gulf of California. In the Grand Canyon it is about 300 feet wide and 30 feet deep, flowing about 2 miles an hour with an average volume of 20,000 cubic feet a second. During freshets the depth, velocity and volume are greatly in creased. In its course of 42 miles through the central or deeper part of the canyon the river falls about 500 feet or 12 feet to the mile. The water contains much sediment, especially in time of flood. Every rain fills the side canyons with rushing torrents which carry into the river a heavy load of debris from the adjoining slopes. Thus has the canyon been excavated and the deepening and widening is still progressing. It began at the surface of the plateau and it will continue until the river reaches a grade so low that it can no longer move the debris; mean.: while the side streams will widen the canyon until its sides become gentle slopes. Under present conditions and without further uplift of the country this will require a million years or more.
The rocks exposed in the walls of the Grand Canyon underlie a wide area of the Arizona Plateau and most of them extend far beyond. The first 3,700 feet of beds, all of which lie nearly horizontal, are as follows : These formations are readily recognized by their color or character as they are practically uniform in aspect and relative position from all points of view.