From 1915 until 1934, Arrowrock Dam stood higher than any other dam and remains an essential part of Boise Valley's irrigation system. Located six miles upstream from here, Arrowrock is 350 feet high and 1,150 feet wide. Built at a cost of $4,725,000 to provide additional water storage to get 2,635 valley farms through dry summer seasons, it had enough extra capacity to take care of more than 1,000 new farms as well. Its 18-mile canyon reservoir holds 280,000 acre feet of water.