Notable among the engineering works calling for courage and daring is the Gunnison Tunnel. This great bore, which in a sense changes physical geography, is excavated under the Vernal Mesa in western Colorado. The river portal is in the famous Black Canyon of the Gunnison, a precipitous chasm 3,000 feet deep, and the tunnel extends for nearly six miles, 2,500 feet below the surface of the Mesa. The outlet is in the valley of the Uncompahgre. By means of a low diversion dam, the waters of the Gunnison are turned into the tunnel and transferred to the desert valley of another stream. The early reconnaissance surveys and examinations and the final work of determining the location of the tunnel were attended with unusual dangers. The exploration of the canyon, which up to that time had never been traversed by man, and the careful and detailed preparation of a topographic map of this rugged region called for genuine heroism. In the former task the surveyors risked their lives for many days in the depths of the gorge, and, in the latter, the engineers performed their duties under conditions of great hazard and peril. The construction forces met and overcame almost every difficulty ever encountered in tunnel excavation. Gas, cave-ins and subterranean springs interposed obstacles throughout the work. At one time a heavy flow of carbon dioxide, or choke damp, forced the workmen to flee for their lives and delayed operations until a ventilating shaft 680 feet deep was sunk. The heavy flows of hot and cold water necessitated the use of large pumps for months at a time. For more than 500 feet the tunnel was driven through a remarkable bed of fossils, consisting of the shells of extinct sea creatures, many of which were of great size. Exposed to the air, disintegration was rapid, and the huge masses of falling rock imperilled the lives of the workmen. Notwithstanding the extraordinary care of the Government to safeguard the employees, a heavy toll of human lives was taken. The excavation work was projected from four adits, three on the Uncompahgre side and one in the canyon, and crews of drill men and assistants simultaneously began boring into the mountain from both sides. When the last charge of dynamite had been exploded and the tunnel was “holed” through, it was found that the line was true within a fraction of an inch. Connecting with the outlet of the tunnel is a large cement-lined canal which conveys the water to the valley ten miles below. Here it mingles with the Uncompahgre, and by means of a complex distribution system of canals and laterals, finally reaches the irrigable lands. The Uncompahgre Valley is one of exceptional scenic beauty, and is blessed with a fertile soil adapted to the growing of a wide variety of products. Its irrigable area is approximately 100,000 acres, more than half of which is now producing two generous harvests.