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.~ ! ~CCElVED FEB 2 7 1991 Mined Land Reclamation Division Pros and Cons of Gravel Pits in Ouray County "-'^~ The residents of the upper Uncompahgre River valley between Ouray and Ridgway face certain long-term problems which are far more serious than that of whether or not a gravel pit is con- structed in their community. Whether they know it or not, they have chosen to build their homes in an area which, from a geolo- gical standpoint, is extremely unstable. This puts them in the unenviable position of not only living on borrowed time, but living on borrowed land as well. The basic problem stems from the fact that the San Juan Mountains to the south are very active geologically. They were created only recently from volcanic upheavals, and have risen quite rapidly. As a consequence, they ace also eroding at a rapid rate. Enormous amounts of sediment are continuously being washed down from the heights and deposited in the valleys. This is the primary reason for the huge amount of gravel along the river between the two towns. But the situation has been aggravated by the mining activity in the San Juans over the last century or so. Clearing of the protective forests has exposed the land to more rapid erosion. The tailings which have been brought Erom underground up to the surface have also increased the amount of erodable material available for removal by surface runoff. Further aggravation comes from the location of the town of Ouray on a giant alluvial fan. Before people settled here, debris washed down from the surrounding cliffs was deposited evenly on all portions of the fan, as succeeding storms filled existing stream channels and diverted the drainages elsewhere. But this could not be tolerated if the people of the town wanted their houses to be secure. The streams have therefore been chan- nelized so they would stay in one place. Sediment which would normally have been spread out over the hillside is washed through the town to the river, which then carries it even further along. Ouray's gain has thus become a loss for the downstream area. The natural aspect of the river below Ouray was once that of a floodplain river meandering across the valley. With each passing flood, the location of the riverbed changed as debris was brought down from the mountains and deposited evenly across the flats. But today the river too has been channelized. The sedi- ment continues to accumulate, and at a rate even higher than before. But it is no longer allowed to spread out. Instead it is artificially confined to a central corridor circumscribed by high gravel ridges on both sides. Buildup of the sediment has raised the bed of the river so that it now flows precariously along a channel which is elevated above the valley floor. As