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- 2- BACKGROUND INFORMATION BLOE RIVER AND TRIBUTARIES Over half of the area in the Blue River basin above Brecken- ridge is above timberline with vegetation limited to alpine tundra. The remaining is land is predomina~tly covered by spruce, fir, plne, aspen, willows, sage and grassland. Breckenridge is located in the upper drainage basin of the ColoradO River. The principal tributary flowing through the town is the Blue River. Minor tributaries discharging into the Blue River in the vicinity of Breckenridge include Lehm3n, lllinois, Sawmill dnd French Gulch"s. The location of Brecken- ridge and its relationship to the streams is shown in Plate 2. Above the town, all the tributary basins draining into the Blue River from the Tenmile Range On the west have been gluc- iated, whereas the tributaries draining into the Blue River from the east have not. As a result of the different geo- logic origins, the tributaries on either side of the Blue River have different hydrologic properties. Sub-basins that have been glaciated have soils developed on glacial muterial. These soils are generally coarse textured and may vary from a very stony or rocky clay to a very coarse textured gravel with boulders and cobble. Infiltration rates and losses for this type of parent material can be high. In the non-glaciated basins east of the Blue River, the soils have been developed on very hard dense igneous and metamorphic rocks. Infiltra- tion rates and 105ses through soils Or debris developed on the igneous rocks may be relatively low. The valley of the Blue River also has been glaciated and land located within a half mile to one mile on either side of the river is covered by glacial material. Consequently, infiltration rates and losses are exceptionally high. The major basin in the Breckenridge area is defined at the point where the Blue River enters Dillon Reservoir. A United States Geological Survey continuous recording stream gage is located approximately 1.5 miles above the reservoir. The drainage area above this gage is 119 square miles and has a mean elevation of 9700 feet above mean sea level. The drainage area above the town of Breckenridge is approximately 55 square miles and has a mean elevation of 10,500 fect above mean sea level. A major hydrologic feature on the Blue River is the Goose )?usture Tarn. The reservoir, commonly referred to as the "Tarn", is located approximately 2 miles above Breckenridge, and has a drainage area of approximately 43.5 square miles. Many other smaller lakes, both natural and man-made, are in the basin. C\) LIlOIa~R':ICo:~t,r~'~hW~'~____ ------ Below the town, the drainage h~sins on either side of the Blue River differ markedly from those above the town. Geologic conditions are different in th"t the I,ldr.,nt mdterials for 50ils are sedimentary rocks or alluvial fans. HydrolOgic properties of soils developed on these materials can be different than those developed on parent materials located above the town of Breckenridqe. Infiltration rates and losses throu~h the soils developed on sedimentary rocks may be relatively low whereas infiltration rates and losses through soils devPloped in the alluvial fans may be moderate to high. However, local varia- tions of infiltration rates and losses may vary considerably within each major area. ct> ~~"~~~O"SUlI"'! 'No:", b9~ee<s, 'IlC Breckenridge is surrounded on three sides by mountain ranges. All the tributaries or sub-basins to the Dlue River in the Breckenridge area have their headwaters on the mountain divides. On t~~ west side of the Blue River is the Ter~ile Range with peak elevations ranging from 12,850 to 14,282 feet. above mean sea level. The Continental ~ivide forms the southern dl\\.1 edstern boundaries of the basin. P~ak ",leviltions along this port Lon of the basi~ range from 12,245 to 13,684 feet above mean sea level. Tributarips to the Alue River with head "'atCl:S on the F.lount<lin divides have the character- istic of steep slo?es and rather long and narrow valleys.