Page:Popular Science Monthly Volume 20.djvu/806

784 feet in height. The last two rivers, entering the valley from the east, cross it immediately and at once take a general northwest course. The Grand flows on toward the northwest until it rounds the end of the Uncompahgre Plateau, when it sweeps slowly around to the southwest, and resumes its normal direction, still hugging closely the left side of the valley.

Southwest of the Uncompahgre Plateau the eye looks out over a stretch of low, arid plateaus, traversed, in deep canons, by the Rio Dolores and its tributaries. This stream is an important branch of the Grand, entering it at the foot of the great valley, after that river has passed around the end of the Uncompahgre Plateau, and just as it plunges into the course of canons by which it passes the Sierra la Sal.

Traveling along the crest-line of the Uncompahgre Plateau, one is interested in observing how sharply the crest-line serves as a water-parting. The drainage toward the west heads in the crest, without cutting it at all. The bluff-wall is everywhere continuous. But in the midst of these observations one is astonished by riding suddenly to the verge of a tremendous gorge, thousands of feet in depth, which apparently comes in from the west, and extends up into the plateau to the northeastward, against the slope and dip of the strata, as far as the eye can reach. Down in the depths he sees a small stream flowing westward. Descending into this cañon, an operation not easily performed at any point, and traversing its bed northeastward, he comes in a few miles to a divide in the canon, and beyond the divide he finds a small stream flowing northeast into the Gunnison. This is the Unaweep Cañon.

The Unaweep Cañon is cut across the Uncompahgre Plateau, from the great valley of the Gunnison and Grand on the northeast, to the low, desert plateaus on the southwest. Its course is nearly southwest, and almost precisely at right-angles to the crest of the plateau. It joins the Gunnison at a point about six miles above the mouth of the latter stream, at an elevation above the sea of 4,600 feet. Tracing its course southwestward, its bed is seen to rise slowly, but not so rapidly as the level of the plateau, so that the cañon increases gradually in depth. The bottom rises to a divide, 7,000 feet above sea-level, and several miles east of the crest of the plateau. The walls at the divide have a height of 1,200 feet. West of the divide, the slope of the bed of the cañon changes slowly, and its descent to the westward does not become very rapid until the crest of the plateau is passed. At the crest, the height of the cañon-walls is 3,000 feet. At the point of junction with the Rio Dolores, the elevation is 4,618 feet above the sea, or practically the same as at its junction with the Gunnison.

The first few miles from the Gunnison the cañon is very narrow, has no great depth, and is cut in soft, recent, sedimentary rocks. This portion might easily have been cut by the small stream now occupying it—a theory which is supported by the fact that the strata here on