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nMI'3"/'3 . . . tion that has not recurred. Because 1941 hydrological conditions were very unusual, this year was excluded from the comparison of monthly flows summarized in Table 9. The exclusion of the 1941 data from the analysis summarized in Table 9 did not affect the estimates of annual flows on the Mancos River, but it did affect the monthly distribution of estimated Mancos flows. Thus, exclusion of the 1941 data resulted in a 600 acre-foot average increase in the estimated Mancos River flow for July, August, and September, with an equal decrease during the other months. A linear regression analysis was made to determine the annual relationship between virgin flows for the Mancos and La Plata rivers for the period for 1938 through 1951. A plot of the annual virgin flows is presented in Figure 3. The linear regression line of best fit through the origin for the data is shown on Figure 3 as a solid line. The regression line is described by the following relation- ship: Annual Mancos Virgin Flow = 1.28 x Annual La Plata Virgin Flow The correlation coefficient for the Mancos versus La Plata annual virgin flows was 0.97, indicating an excellent relationship between the two gages. This correlation occurs primarily because the two drainage areas are adjacent to each other, with the Mancos and La Plata rivers both draining all of the La Plata Mountains. As noted in Section II, USGS records for the Mancos river gages were only "fair," meaning that the error in the daily records was less than 15 percent. USGS records for the La Plata River gage was considered to be "good," meaning that the error was less than 10 percent. Such error can account for much of the scatter in the plot of Mancos versus La Plata flows on Figure 3. Monthly virgin flows for the sum of the West, Middle, and East Mancos River gage sites were estimated by the following method: Monthly Mancos Virgin Flow = 1.28 x Monthly La Plata Virgin Flow x Mancos Correction Factor -27- ,