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The dissolved-solids concentration in the Cimarron River (site 16) was 374 mg{L. This relatively large value is most likely due to the Mancos Shale ~ that underlies the lower reaches of the river. The dissolved-solids en concentration, adjusted for the effects of Blue Mesa and Morrow Point ~ Reservoirs, in the Gunnison River below Gunnison Tunnel (site 17), was 00 137 mg{L at an adjusted flow of 420 ft3{s. The dissolved-solids concentration in the Smith Fork (site 18) was 2,310 mg{L. This large value is probably a result of the large area of Mancos Shale that underlies the drainage. The base flow in the Smith Fork was only 2.8 ft3{s. The adjusted dissolved-solids concentration in the Gunnison River above the North Fork (site 19) was 145 mg{L. This is only slightly greater than the value below the Gunnison Tunnel and reflects' the small discharge from the Smith Fork and other tributaries. Igneous and metamorphic rocks underlie this stretch of the main stem of the Gunnison River, but the Dakota Sandstone and Mancos Shale underlie most of the tributaries. No water-quality gaging stations are in this subbasin and, therefore, no comparison of sample data with historical data was possible. The upper Gunnison River subbasin contributed an estimated 28,400 ton{yr of base-flow salt load adjusted for reservoir effects. The estimate is relatively low considering the combined measured base-flow discharge of 190 ft3{s contributed by the subbasin drainage. The low value is due to the 'predominance of igneous rocks beneath the drainages north and south of Blue Mesa and Morrow Point Reservoirs. The Cimarron and Smith Fork Rivers, which are underlain by areas of Mancos Shale, contributed an estimated 7,700 and 6,400 ton{yr of salt, respectively. These two rivers contributed about 50 percent' of the estimated annual base-flow salt load produced by the subbasin but only about 13 percent of the measured base-flow discharge from the subbasin. North Fork Gunnison River This ,subbasin includes the drainage area of the North Fork Gunnison River (fig. 10). The Wasatch Formation of Paleocene and Eocene age is at higher altitudes, the Mesaverde Group at middle altitudes, and the Mancos Shale at lower altitudes. Intrusive igneous rocks are locally present along the southern and eastern parts of the subbasin. Five sampling sites were selected in this subbasin (figs. 10 and 13; table 3). Dissolved-solids concentration were 182 mg{L in Muddy Creek (site 20) and 93 mg/L in Anthracite Creek (site 21). These creeks drain predominantly the Wasatch Formation. The dissolved-solids concentration in Cottonwood Creek (site 22) was 4,640 mg{L, in Leroux Creek (site 23) 1,090 mg{L, and in the North Fork Gunnison River near the mouth (site 24) 1,170 mg{L. These large values are due to salt from the Mancos Shale that underlies the lower part of the subbasin. No adjustment was made for the effects of Paonia Reservoir. No water-quality gaging stations are located within the subbasin; and, therefore, no comparison of sample data with historical data was possible. The North Fork Gunnison River subbasin contributed an estimated 72,600 ton{yr 40