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Table 8. Annual precipitation data at four stations near the Hunti ngton W sediment basins. W ~ STATION Hi awa tha Castle Dale Ferron Price Warehouses 0) (years record) ( 14) (15) (15) ( 10) Annual average, cm 35 17.8 20.8 20.6 Annual average during 1 ife of p1 ugs 29.5 15.5 17.8 17.8 Resu1 ts Results of the sediment basin stUdy are provided in Table 8. Sediment accum- ulations in the retention plugs averaged 7.75 t/ha/yr (3.4 tons/acre/yr). The highest sediment accumulation was from the steepest basin. However,sedi- ment accumulations did not correlate well with any of the measured watershed characterstics. Annual precipitation during the 6-7 year life of the plugs a$ measured at nearby stations was not significantly different (~ =0.05) from the long-term average for the area (20.1 cm)(Tab1e 7). Mancos shale sediments yield roughly 30 kg of salt per metric ton (t) of sediment (a 3% salt content in sediments)(USDI, 1978). Thus, the estimated average annual salt yield from the stUdy basins was 0.23 t/ha/yr (0.10 tons/ acre/yr). Conclusions Six to seven years are not long enough to accurately determine long-term sedi- ment and salt yields from shale badlands in arid settings. Large, infrequent storm events can cause a disproportionately high rate of erosion. However, the average annual sediment yie1d--7.75 t/ha/yr (3.4 tons/acre/yr)-- and salt yie1d--0.23 t/ha/yr (0.10 tons/acre/yr)--represent a reasonable estimate of long-term salt and sediment yields from Mancos shale badlands in arid envi- ronments. The values compare favorably to sediment and salinity yield esti- mates calculated for other regions on Mancos shale. Salt yields are roughly two times higher than those estimated at Badger Wash, Colorado. This iseJ(- pected, however, because study basins at Badger Wash are less saline, less steep and more vegetated than those at Huntington. Sediment yields at Huntington are roughly 70% higher than those determined by the Soil Conser- vation Service (SCS) (USDA Soil Conservation Service, unpublished data) for five small basins at Indian Wash, Colorado. Again, the Indian Wash basins have milder slopes than those at Huntington and could be expected to produce somewhat less sediment (Table 9). In another unpublished report, SCS estimates erosion from steep Mancos shale badlands to be 20 to 34 t/ha/yr (9 to 15 tons/acre/yr). This is higher than that measured at Huntington but, presumably, was determined in part from data that contained a large, infrequent storm which contributed a large proportion of the total erosion. 29