SNAKE RIVER DIVISION. Mr. A. D. Foote, division engineer, was assigned to the charge of this division, and commenced field work in June, 1889. He immediately organized a party under the charge of Mr. A. W. Wiley, assistant engineer, and began the work of surveying canal lines to be diverted from the Snake River below Eagle Rock. Mr. Wiley was engaged on the field and office work connected with these surveys until March 14, 1890, when he resigned. On the same day Mr. F. J. Mills was engaged as assistant engineer, and continued the survey of the Snake River canal lines until the end of August, 1890, at the close of the irrigation surveys. After starting Mr. Wiley's party in July, 1889, Mr. Foote undertook a personal reconnaissance on the headwaters of the Snake in search of reservoir sites. (See Pl. XCVI.) In the performance of this work he examined the South Fork of the Snake River, on which he found the Swan Valley reservoir site, which has a storage capacity of about 1,500,000 acre-feet. Higher up, near the head of the same fork, at Jackson's Lake, a second reservoir site with a capacity of 500,000 acre-feet was discovered. On the Falls River branch of the North Fork, the Falls River reservoir site, with a capacity of 500,000 acre-feet, was discovered, and a preliminary examination of it made. Mr. Foote reports that there is a possibility of finding one or two other reservoir sites on the South Fork or its tributaries, but that in all probability these will be unnecessary, since the large sites just described will doubtless prove capable of storing all the water available. Swan Valley is of dimensions so enormous that it can probably be made into one of the largest reservoirs in the United States. It is about 8 miles long by 4 miles wide, and very level. Through the center of it the Snake River winds with a slow velocity and very slight fall. The walls bounding it are steep and high, and the outlet is a narrow gorge with perpendicular rock sides and a rock bottom. A dam can easily be constructed across it 100 feet in height if necessary. Into this valley the drainage of nearly the entire South Fork of the Snake River passes. From the reconnaissance it is found that the area of this valley averages 32 square miles,in which water can be impounded to a depth of 100 feet, and about 25 square miles to a depth of 50 feet. A loose rock dam 125 feet in height will store all the water entering this valley, thus avoiding the expense of constructing a masonry dam. Immediately above Swan Valley is another reservoir site of nearly equal capacity; and without examining in detail Mr. Foote is of ομ opinion that several good sites can be found on this river between Swan Valley and Jackson's Lake. The Swan Valley dam, for holding back a million and a half acre-feet, is in such a position as to avoid the necessity of building a waste weir. Raising the water will cause the surplus to flow over a low granite-bound gap to one side of the present channel, thus affording a natural waste weir. By this favorable location the cost of the dam, although large, will not exceed 33 cents per acre-foot. This valley has a watershed of about 5,365 square miles, the run-off of which is at least 4,000,000 acre-feet. Jackson's Lake, with a watershed of about 840 square miles, the run-off of which is not less than 9,000,000 acre-feet, would need a dam only about 20 feet in height to impound 500,000 acre-feet. Such a dam will not cost more than 20 cents per acre-foot. The Falls River reservoir site is also favorable, and the dam should not cost over 20 cents per acre-foot. The surveys for the Pocatello Canal line include a canal to be diverted from the Snake River at Eagle Rock. This was surveyed for a distance of 100 miles, in the course of which it crossed the Blackfoot River, and farther on the Portneuf River at Pocatello, finally terminating and tailing into the Snake River above American Falls. It was intended that this canal should have at its head a bed width of 50 feet, with a depth of 71⁄2 feet of water. At this point its calculated velocity of flow was 3:46 second-feet, and its discharge was estimated to be 1,492 second-feet. This canal, if built, will command 216,400 acres of arable land, all of which has excellent soil. Two canal lines were surveyed from the American Falls, on the Snake River, the first or lower one having a total length |