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slopes with bright, clear days and warm sunshine attracts winter sports enthusiasts throughout the winter months. Other winter vacationers are attracted by mild winter days in the sunshine and warmth of the desert. PHYSIOGRAPHY AND GEOLOGY " Physiography Most of the San Juan River Basin lies within the northern part of the Navajo section of the Colorado Plateaus physiographic province, an area of plateaus underlain by relatively horizontal sedimentary rock layers which form mesas, buttes, cuesta ridges, and rock terraces separated by broad, open valleys and occasional canyons. An area in the northwestern part of the basin lies within the Canyon Lands section of the Colorado Plateaus province, and narrow areas along the northeastern margin of the basin are occupied by the San Juan mountains portion of the Southern Rocky Mountains physiographic province. Elevations vary from about 3,600 feet at Lake Powell along the lower reaches of the San Juan River to 14,084 feet on Windom Mountain in the Needle Mountains area in the central portion of the San Juan Mountains northeast of Durango, Colorado. The San Juan Mountains are a well-defined area of rugged mountains rising abr.uptly from the mesa and foothill surfaces of the adjoin- ing Colorado Plateaus province and containing numerous peaks over 13,000 feet. They consist largely of volcanic rocks in more or less horizontal layers overlying older sedimentary rocks. Most of the area has been glaciated, and such typical features as knife- edge ridges, cirques, and rock streams are common. r The most rugged part of the San Juan Mountains is known as the Needle Mountains, and here the mountains consist mainly of older, more resistant crystalline rocks such as granites, gneisses, and schists. At the southwestern end of the San Juan Mountains are two smaller ranges - the Rico Mountains and the La Plata Mountains. Both are domed uplifts of sedimentary rocks intruded by igneous rocks. Both groups have many peaks more than 12,000 feet. The main part of the San Juan River Basin, lying within the Colorado Plateaus province, is an area of diverse topography containing num- erous mesas and plateaus underlain by resistant. rock layers, exten- sive areas of plains and broad valleys with gentle slopes cut in softer rocks, gently. sloping ridges, hogback ridges, high dome moun- tains, some rough badlands, and a few deep, narrow canyons. The most predominant features of this area are the scattered mountains which, in most cases, were formed by the doming of sedimentary rock layers by igneous intrusions. These include the Ute Mountains in 111-4