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<br />July 1993 -9- 923-2515 <br />10 acres. This reach is a broad, flat azea of decreased stream gradient compared to the adjacent <br />reach upstream. The channel is characterized by a series of fight meanders. <br />3.4 Grass~Creek <br />The headwaters of Grassy Creek from sec. 32, T. 5 N., R. 87 W. to Windy Point Road, in <br />sec. 15, T. 5 N., R. 87 W., were mapped as part of the previous, 1990 Golder, ACZ, <br />Keammerer study. The geology of the headwaters of Grassy Creek are not discussed in this <br />report. The portion of Grassy Creek mapped during this study is from Windy Point Road <br />downstream to the confluence with the Yampa River. The reach of Grassy Creek that extends <br />from Windy Point Road downstream to within approximately 1000 feet of the northern boundary <br />of sec. 10, T. 5 N., R. 87 W. (Figure 1) has been mapped as alluvium (approximately 75 <br />acres). This area is flat and exhibits a sharp break in topography from the adjacent slopes. In <br />• addition, the channel undergoes considerable meandering throughout this reach of the drainage. <br /> <br />An alluvial fan is mapped at the boundary of sections 3 and 10, T. 5 N., R. 87 W. The reach <br />of Grassy Creek that is located between the area mapped as alluvium in sec. 10, T. 5 N., R. <br />87 W. and the azea mapped as a landslide, located in the northern half of sec 3, T. 5 N., R. <br />87 W. (Figure 1) has been mapped as undifferentiated valley fill (approximately 30 acres total). <br />The steep, narrow valley walls and colluvium present in the valley hinder determination of the <br />genesis of the material in the valley floors. <br />The azea which has been mapped as a landslide is probably not the result of a catastrophic event. <br />Rather, slope instability is likely the result of basal creep of the Twenty-Mile Sandstone on an <br />underlying shale layer. The valley floor is narrow and colluvium is not readily distinguished <br />from alluvium along this reach of the drainage. Upstream of the landslide (N'h sec. 3, T. 5 N., <br />R. 87 W.) is another small alluvial fan. <br />Golder Associates <br />