A MAMMOTH DAM. A dispatch from Colorado Springs, Colo., dated December 3, is to the following effect: The San Luis Valley Irrigation, Land and Power company will build a dam several feet higher than the Cheesman dam, and, therefore, the highest in the world. The site is a gorge at Terrace, on the Alamosa river, fifteen miles below La Jara. The first hundred feet of the dam will close a twenty-five-foot opening between walls of solid rock. The rock walls then separate, widening to 250 feet. This opening will be closed by the next hundred feet of dam, which will extend ten or more feet above the summit, a total height of 210 feet. The dam will be a quarter of a mile long. The reservoir thus formed will cover a tract 200 feet wide by three and a half miles long and 200 feet deep.