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• The only change in the wildlife situation from that of the 1979 study is the grizzly bear. Prior to 1979 the last sighting of a grizzly in Colorado was near Emerald Lake in 1951. However, during 1979 while the original study report was being written, a grizzly sow was killed in the South San Juan Wilderness. GEOLOGY Continuous mountain-building revolutions are shown in the rocks and formations of the river corridor. Six formations of the Precambrian era exist in the area. Little is known of the geologic processes during the long period between the Precambrian and Tertiary periods. The sedimentary rocks and formations of these periods are not found in the valley. During the Tertiary period, the area was subjected to disruption of mountain building forces. Volcanic series of the period laid down nine formations and ash flow units. The violent volcanic series were separated by glacial episodes, block faulting, uplifting, and warping. VEGETATION The 1979 study developed a series of wildlife-vegetation associations. The following table summarizes the broad cover types within the wild and scenic •river study area. LOS PINOS BASIN COVER TYPES Int Acres Percent of Area Spruce Fir (Mixed 7 Pure Stands) 52,400 84% Douglas-fir 1,700 3% Aspen 700 1% • Stands of Dwarfed Spruce at Timberline 1,100 2% Rock and Dry Grasses 5,700 9% Willow and Wet Grass Bogs 300 Less than 1% Lakes and Ponds 600 Less than 1% The Federal Register (40-127, V) contained a list of 23 endangered and 17 threatened candidate plant species for Colorado as determined by the Smithsonian Institute. It still remains to be determined where, or if, any of these species are present in the river corridor. The forested areas of the river valley are not considered for timber harvest because the river is in classified wilderness.