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"'~33 002D from 10 to 14 inches (250 to 360 mm) of precipitation annually. A comparison of figures 5 and 8 shows that the areas of large sediment yield are also those areas which receive from 10 to 14 inches (250 to 360 mm) of precipita- tion annually. Sediment yields decrease eastward as precipitation Increases, and the smallest sediment yields are from those areas that receive the most precipitation. Comparison with Estimates by Other Investigations A sediment-yield map of Colorado was prepared by the Colorado Land Use Commission (1973) using the Pacific Southwest Inter-Agency Committee (1968) or PSIAC method. This method develops a numerical rating of the potential erodlbll ity of a watershed in nine categories, as shown in table 3. The erosion rate is estimated by comparing the numerical score with the measured erosion rate of drainage basins with a similar score. Sediment yields were computed at the 17 gaging stations in the Yampa River basin from the Colorado State map. The percentage of a subbasin in each level of erosion was determined and then the average erosion rate fo~ the drainage. In order to obtain an accurate estimate at each station, the average erosion rates must be adjusted to the drainage area. Brune (1948) showed that, other factors being constant, sediment yields (y ) vary inverse- ly with drainage area (A) to the 0.15 power: S Ys (A2)O'IS ~"'- Y Al s2 The erosion rate determined by the PSIAC method applies to a drainage area of 1 ml2 (2.59 km2). Hence, the average erosion rate (Yl) for a given drainage area must be multlpl ied by (~rlS to give the estimated sediment yield (yA) at the gaging station. A comparison of the sediment yields computed In the investigation (abscissa) with the sediment yields determined by the PSIAC method (ordinate) is shown in figure 9. There is considerable scatter around the line of agreement, and no consistent relation between the two methods Is apparent. Thus, although sediment yields estimated by the PSIAC method may agree with the average of several measured sediment yields, the PSIAC method probably will not provide a good estimate of the actual sediment yield for a specific location. The measured sediment yields compared with the Langbein-Schumm mean-annual precipitation for each In the Yampa River (1958) relation shown of the 17 subbasins basin also may be on figure 6. The was determined from 22 , ! .-c.