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flows north and passes through a small portion of the northeastern section of Castle Rock. It, also, is an ephemeral stream. The climate of the Castle Rock area is high, inland continental, modified by the Rocky Mountains immediately to the west and Palmer Lake Divide to the south (Reference 3). Precipitation is light, with an annual average of 15 to 18 inches. Annual totals vary substantially because a large part of each yearly total is from summer thunderstorms. Temperatures in the Castle Rock area range from a high of slightly more than 1000p to lows of approximately - 350P. The mean annual temperature is 470p; the mean summer tempera- ture is 660P. Loamy and sandy soils exist on the flood plains and terraces in the Castle Rock area (Reference 5). Terrain in these areas is nearly level to gently sloping, and vegetation is mostly grass, with a few trees. On either side of the East Plum Creek drainage- way, the terrain is gently sloping to moderately steep, with sandy and gravelly soils on the uplands. Vegetation is mainly grass, with some Gambel Oak, mountain-mahogany, and ponderosa pine trees (Reference 6). 2.3 Principal Plood Problems The Town of castle Rock has experienced flooding from the overflow of East Plum Creek on several occasions, with the most severe damage occurring in 1965. Plooding took place in May 1864 and June 1921, but no determinations of flows in East Plum Creek are available. A flood on September 9-10, 1933, was caused by heavy rain on the divide separating Cherry Creek from Plum, Big Dry, and Little Dry Creeks. In an investigation of this flood, the office of the State Engineer made a slope-area determination of the flow in Plum Creek (Reference 7) and found it to be 5,500 cubic feet per second (cfs). High-intensity, heavy rains were recorded at three locations in the Plum Creek basin on the afternoon of June 16, 1965. OVer 12 inches fell near Castle Rock and over 14 inches fell near Palmer Lake and near Larkspur in approximately 4 hours. East Plum Creek and West Plum Creek crested at 126,000 and 36,800 cfs, respectively, during the afternoon. The unit runoff above the site on East Plum Creek just downstream from Castle Rock was 1,170 cfs per square mile, for a drainage area of approximately 108 square miles. West- ern tributaries of West Plum Creek and all tributaries of Plum Creek downstream from Sedalia were outside the high rainfall areas and contributed little or no runoff during the flood. Large cut banks, particularly along East Plum Creek, were left after land had been washed away. Much of the Town of Castle Rock was inundated, and service was disrupted to approximately 100 tele- 5