Adjoining The Bob Marshall Wilderness Area to the east is the Gibson Reservoir. Although the initial conversations about the creation of the Gibson Dam began in 1907, construction did not start until 1926, in part due to its remote location. Even then the nearest railroad was still 23 miles away in Augusta. Gibson Dam was the first American dam to be analyzed and designed according to the trial-load method. The trial-load method relies on mathematical equations to determine stresses and strains acting on a dam. This method would later be used in the design of the Hoover Dam on the Colorado River. Gibson Dam, an imposing, concrete half-moon, standing 199 feet high with a crest length of 960 feet, is able to store 99,000 acre feet of water in its reservoir! Its base is approximately 117 feet wide and tapers to 15 feet wide at the top. Construction of the Dam was completed in 1929, and it was the last of the major irrigation projects in the Sun River drainage. The Gibson Resevoir is within a couple of miles of the Sun River Ranch and just under 30 miles from Shortridge Ranch.