Students of geology and physical geography have long been aware of these facts. It is well known that, under the modifying influences of man, the streams of any region redeemed from the wilderness are changed in many important characteristics. In flood times their volumes are excessively increased and their powers of destruction multiplied. In seasons of drought, some streams that were perennial before man modified the surface of the country become entirely dry; the smaller navigable streams have their periods of navigation shortened, and the great rivers run so low at times that navigation becomes more and more difficult during dry seasons; in multiplied ways these effects are demonstrated. While in the main the artificial changes wrought by man on the surface are productive of bad results in humid regions, the changes are chiefly advantageous to man in arid regions where agriculture is dependent upon irrigation, for here the result is to increase the supply of water. Mr. Gilbert, while engaged during the past season in studying the lands of Utah, paid especial attention to this subject, and in his chapter has more thoroughly discussed the diverse special methods by which increase in the flow of the streams is caused by the changes wrought by man upon the surface of the earth. His statement of facts is clear, and his conclusions are deemed valid. CHAPTER VI. THE LANDS OF UTAH PHYSICAL FEATURES. A zone of mountains and high plateaus extends from the northern nearly to the southern boundary of Utah Territory. The Wasatch Mountains constitute the northern portion of this zone, the High Plateaus the southern. This central zone has a general altitude above the sea of from nine to eleven thousand feet. Many peaks are higher, a few reaching an altitude of about twelve thousand feet. On the other hand many cañons and valleys have been excavated by the running waters far below the general level thus indicated. The Uinta Mountains stretch eastward from the midst of the Wasatch. This region is a lofty table land carrying many elevated peaks whose summits are from twelve to nearly fourteen thousand feet above the level of the sea. This is the highest portion of Utah, and among its peaks are the culminating points. South from the Uinta Region, and from the southern extremity of the Wasatch Mountains, another elevated district extends east-southeast beyond the borders of Utah. This table land is cut in twain by two great gorges of the Green River--the Cañon of Desolation and Gray Cañon. The eastern portion is called East Tavaputs Plateau, the western West Tavaputs Plateau. Between the Uinta Mountains and the Tavaputs table land is the Uinta-White Basin, a low synclinal valley, drained by the Uinta and its ramifications on the west, and the lower portion of the White River on the east.