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Show tary, the Gunnison, flows southwest from the heart of the Rockies through broad sagebrush valleys to this junction point. The Colorado River beyond this junction plunges into a wild and fantastically eroded land of winding gorges and sandstone mesas whose vast expanses are punctuated at irregular intervals by the isolated, steeply upthrust masses of the Henry, Abajo, and Navajo Mountains. With the exception of the mountain summits, which are cool and moist, the greater portion of the area receives but little snowfall in winter and is characterized by a long, warm summer season. Average temperatures are higher than those of valleys to the north, in conformity with the decrease in latitude, but lower than those of deserts to the south. The annual precipitation ranges from about 6 to 14 inches, with the greatest amount coming from thunderstorms during July and August. This desolate but spectacularly scenic sandstone area is referred to in this report as the Canyon Lands of southeastern Utah. Into it from the east, through a deep meandering gorge, flows the turbid San Juan River which, with its tributaries, drains a far- reaching area, including the La Plata Mountains, the San Juan Mountains and other lesser ranges on the Continental Divide, the Chuska Mountains, and enormous areas of mesa land in the interior of the basin. From the Wasatch and Aquarius Plateaus on the west come other, but lesser, silt- laden streams, all carving the deep, winding canyons which have given this country its name. The Canyon Lands terminate, approximately, at a third, intermittent barrier formed by the Paria Plateau, Black Mesa, and the Chuska Mountain mass. Southwest of this third barrier lies the great valley of the Little Colorado River and the adjacent House Rock Valley- a semidesert grassland, pifion pine, and juniper country which, in spite of its enormous area, contributes but a meager stream flow because of the sparse annual rainfall and snowfall. Winters are mild and summer temperatures about the same as in the Canyon Lands. South and west of the Little Colorado River, the last great highland barrier extends in a vast curve '^^'^^/^•^^^•• r.. Figure 4.- Canyon Lands of southeastern Utah- looking over the junction of the Green and Colorado Rivers to the Henry Mountains from Dark Canyon Plateau. |