The Crystal River drains the western slope of the Elk Mountains, a relatively small range in the southern Rocky Mountain province, and flows into the Roaring Fork 13 miles southeast of Glenwood Springs, Colo. The lower 7 miles of the valley is cultivated, but upstream from this stretch the valley is narrow and is used mainly for summer grazing and recreation. Above the mouth of Thompson Creek, numerous dam sites are available, but the narrow valley and steep gradient do not favor storage for regulation of streamflow. The potential power from the natural flow of the stream in an average year is estimated to be 4,750 kilowatts for 95 percent of the time; 5,102 kw for 90 percent of the time; 10,570 kw for 50 percent of the time; and 36,940 kw at mean flow. Using the regulated flow resulting from the utilization of reservoirs at Marble and Redstone, the potential power is estimated to be 26,510 kw for 90 percent of the time and 27,810 kw for 50 percent of the time.