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<br />. <br /> <br />. <br /> <br />. <br /> <br />Or.-....5 <br />:..1..1':'0 <br /> <br />CMPTER II <br /> <br />DESCRIPTION OF STUDY AREA <br /> <br />Location <br /> <br />The San Juan County study area includes all of San Juan County and <br />a part of Grand County, Utah, and minor parts of Dolores, San Miguel, <br />Montrose, and Mesa Counties J Cola., as shol..Jn on the frontispiece !rap. <br />The triangularly shaped area, larger than the State of Massachusetts, <br />lies mostly between the Colorado River and its tributaries, the San <br />Juan and Dolores Rivers. Its 8,960 square miles are distributed by <br />counties as shown below. <br /> <br />San Juan County, Utah <br />Grand County, Utah <br />Dolores, San Miguel, Montrose, <br />and Mesa Counties, Colo. <br />Total <br /> <br />Square miles <br />7,884 <br />462 <br /> <br />614 <br />F,9ti5 <br /> <br />Physical Characteristics <br /> <br />The unique and spectacular geologic features of the San Juan Area <br />are of interest to both the casual visitor and the trained geologist. <br />The landscape provides the best illustration known to man of the geolog- <br />ical processes involved in its formation. In approxin~te historical se- <br />quence these processes were (1) deposition of material by wind and water, <br />(2) consolidation, (3) deformation by folding and faulting, and (4) nor- <br />mal erosion, later accelerated by a general uplift. Volcanic action no <br />longer occurs in the area, but the formations are still changing from <br />frost and erosion processes. <br /> <br />The diverse landscapes include arches, <br />plains, nearly vertical escarpments, mesas, <br />sected canyonso <br /> <br />spires, needles, broad <br />buttes, and intricately dis- <br /> <br />The area is near the center of the vast Colorado Plateau Province, <br />which includes major portions of Utah, COlorado, Arizona, and New Mexico. <br />It includes the east-central portion of the Canyonlands subdivision of <br />the province. A characteristic feature of the Canyonlands is its horizon- <br />tal rock structure wasting at the edges by erosional processes, leaving <br />steep escarpments. In places a series of beds up to 1,000 feet thick has <br />eroded away for miles while the remaining portion has remained largely <br />intact. Usually the retreating escarpment is not a straight, vertical <br />front but is fringed by numerous canyon tributaries. Thus, weathering <br /> <br />11 <br />