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<br />- 13 - <br /> <br />development, and with the least possible disturbance of the precarious <br /> <br />slopes and natural vegetation cover. <br /> <br />Major Mudflow Fan Area (2) <br /> <br />General <br /> <br />This major feature is very evident on both topographic maps and <br /> <br />aerial photographs because it has the classical form of an alluvial <br /> <br /> <br />fan, (figure 1, plate 2, plate 3). It is called a mudflow fan in this <br /> <br /> <br />report because it appears to be built almost entirely by a succession <br /> <br /> <br />of mudflows with only minor and local reworking by running water. At <br /> <br />the present time, Carbonate Creek is routed along the east margin of the <br /> <br />older fan and Slate Creek runs along its west margin. It is virtually <br /> <br />certain that in the geologic past both have contributed to the deposi- <br /> <br />tion of the older fan which is more than a mile wide, and estimated to <br /> <br />be at least 175 feet thick near the Marble townsite. Deposition of <br /> <br />this fan has deflected the course of the Crystal River southward, and <br /> <br />mudflows have periodically dammed the river. Beaver Lake is a man-made <br /> <br />enlargement of ponding caused by mudflows on Carbonate Creek. More <br /> <br />detailed features of the main mudflow fan will be discussed separately <br /> <br />below. Plate 3 is a detailed topographic map of the mudflow fan area. <br /> <br />'. <br /> <br />. .slate Creek Mudflow (2a) <br />Slate Creek enters the area near the apex of the major fan, and <br /> <br />follows an entrenched course along its western edge (plate 1). This <br /> <br />is a highly erosive channel, and the banks are oversteepened to the <br /> <br /> <br />extent of being potentially very unstable, (figure 2). In the lower <br /> <br /> <br />reaches, starting about 2,bOO feet north of the Crystal River, the <br />