On the arid Mountain Home Plateau of Idaho more than 400,000 acres of arable land is largely unused except for grazing. The Boise Valley, adjoining on the north, was reclaimed from similar land and irrigated with Boise River water. The productivity of about 100,000 acres of the valley land is lowered or threatened, however, by an ever-rising water table, caused to rise by infiltration of excess irrigation water. Surface drains alleviate the drainage problem but areas of water-logging, alkaline land, and inferior vegetation continue to spread.