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Mormon Settlements and the use of Water
Early Mormon Pioneers, led by Brigham Young, changed the desolate deserts of the valleys of the intermountain west into green, productive farmland. The construction of canal systems, which in the Lake Bonneville basin took advantage of existing shoreline benches on the edges of valleys to feed water to the former lake bottoms below, allowed mixed farming in mountain valleys which had formerly supported only sagebrush and grasses.

"since the Mormon farmers from Utah... had pushed ahead into the agricultural lands of Southern Idaho, irrigation commenced to be introduced, and I must give my fullest regard and admiration to the skill and the perseverance of these first irrigators and re-clamationists, who were teaching new settlers how the desert lands could be made blooming like the rose...The reclamation of the upper Snake River valleys, in its first work almost solely performed by the Mormons, is one of the examples of their wonderful ability as colonizers of a good deal of the western country. As our early Pioneers they were strong and patient and with firm belief in the protection of a divine power to enable them to endure the hardships and sufferings attendant upon the early settlement of what are now the prettiest, the richest and the most promising valleys of Idaho."   Oscar Sonnenkalb (in Harstad, 1972, p.8,1516).

As Mormon settlers moved into southern Idaho in the 1860s, it was obvious that the land had to be irrigated for farming to be feasible. Irrigation canals were built in Cache and Malad Valleys soon after settlement. Much of the country too high or too rugged to irrigate became grazing land.

In the early 20th century, the determined efforts of the Last Chance Canal Company to bring irrigation water to the Grace area in Gem Valley were opposed by the Utah Power and Light Company, which sought the water for hydroelectric generation. The historic Dietrich Decree of 1919 awarded water rights to the Mormon farmers who had filed on it first. One of the primary tenets of Western water law (first in time is first in right) had been established (mcCarthy, 1987).

Irrigation of the Snake River System
North of the Mormon country, there were limited attempts to establish irrigation systems. Rev. Henry Spaulding at the Lapwai Mission, up the Clearwater River from Lewiston, developed some irrigation during the 1830s and 40s as he tried to turn the Nez Perce of the area into farmers. The first Mormon settlement in Idaho, in 1855 at Fort Limhi along the East Fork of the Salmon River, built an irrigation system.

Oneida Narrows Reservoir, north of Preston, looking southeast from high above the west shore. The dam is at the narrow constriction in the distance. The rocks here belong to the Late Proterozoic and Cambrian Brigham Group, (august, 1985).

Through the sagebrush desert of much of southern Idaho, the Snake River flowed full of water along treeless plains, adjacent to vast fields of fertile soil which were unproductive because the nearby waters could not be diverted. The Snake drains a huge area which usually has heavy snows in the winter and from which a number of tributaries flow.

An area several hundred miles long north of the Snake River between Henry's Fork in eastern Idaho to the Malad River (the continuation of the Wood River) at Hagerman Valley contains almost no surface streams that persist as far as the Snake. Extensive lava flows block the pre-existing drainage channels. In these areas are large underground water supplies contained within the Snake River Plain Aquifer.