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Most of the streamflow in the Arkansas River comes from the tributaries on the western side of the upper basin. These tributaries drain the high mountains along the Continental Divide, where most of the winter precipitation accumulates. Station 07083000 (Halfmoon Creek near Malta) is typical of those tributaries not affected by transmountain diversions. As seen on figures 95 and 96, the runoff from these tributaries is much greater than fru", any other type of tributary. The frequency CUrve of monthly runoff (fig. 95) illus- trates the runoff variability. In any month, the probability of the monthly runoff being equal to or less than 0.1 in. is 1 percent, and the probability of the monthly runoff being equal to or exceeding almost 10 in. is 1 percent. Much of that variation is explained by the seasonal flow pattern that occurs every year (fig. 96). For example, the mean February runoff is 0.17 in., compared to the mean June runoff of 6.0 in. After the snowmelt peak in June, a general recession of streamflow occurs through December (fig. 96). The tributaries on the eastern side of the upper basin and most of the tributaries between Salida and Pueblo have much less runoff than those on tne western side of tne upper basin. Few of these tributaries have a long period of record upon which generalizations about their flow can be based. However, station 07099100 (Beaver Creek near Portland) has 11 years of record that illustrate characteristics thought to be similar to many of these tributaries. Runoff at this station is highly variable (fig. 95). The probability in any month of the monthly runoff being equal to or less than about 0.0001 in. is 1 percent, while the probability of the monthly runoff being equal to or exceeding about 1 in. is 1 percent. Station 07099100 shows a wide range between minimum and maximum for every month (fig. 96). The one standard deviation band goes to the bottom of the plot because the standard deviation of every month is greater than its respective mean. Tne general shape of the montnly curve still shows a recession after the snowmelt peak, but the peak is in May, not June, and the recession ends in October. Station 07096000 (Arkansas River at Canon City) is typical of the main- stem stations upstream from Pueblo. This station nas a remarkably small range in flow (fig. 95). As is the case with the western tributaries, much of the variation occurs each year as part of the seasonal cycle (fig. 96). The small- est monthly mean runoff is 0.11 in. in March; 0.80 in. in June is the largest. The fact that almost all the flow comes from the western tributaries is demon- strated by the fact that the monthly runoff hydrograph for station 07096000 (fig. 96) is similar to that of station 07083000, although their drainage areas are 23.6 mi2 for station 07096000,.and 3,117 mi2 for station 07083000. Five major tributaries enter the Arkansas River downstream from Pueblo: Fountain Creek; St. Charles River; Huerfano River; Apishapa River; and Purgatoire River. The headwaters of these tributaries are in mountainous regions that contribute considerable runoff. However, much of that flow is lost as these streams cross the prairie before joining the Arkansas River. The flow entering the Arkansas River from each of these tributaries is thunderstorm runoff and return flows and waste water from irrigation canals. Station 07119500 (Apishapa River near Fowler) was selected as representative of the runoff contributed to the Arkansas River by these tributaries. In any month, the probability of the monthly runoff being equal to or less than about 0.001 in. is 1 percent, and the probability of the monthly runoff being greater than or equal to about 0.3 in. is 1 percent. The slope of this 64