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.
The discharge of the Uncompahgre River was quite inadequate for the
irrigable lands in the valley, which had been brought under the ditches
constructed before the passage of the reclamation act, and failure of
crops occurred frequently during the low water periods. In addition
there were thousands of acres of desert land in the valley doomed to
aridity unless the water supply could be supplemented. The Gunnison
River, flowing uselessly in its profound canyon on the other side of
the range, was drawn upon by means of the tunnel, and an abundance
of water is now assured for all the lands included in this project.
Agriculture here is exceedingly diversified, and in many sections, is
intensive. The products of the soil range include alfalfa, cereals,
sugar beets, potatoes, onions, peas, beans, and other vegetables,
peaches, pears, and apples. Surrounding the valley are vast areas of
fine grazing lands included in national forests, which furnish summer
pastures for thousands of cattle and sheep. The rapid settlement of the
farm lands has been followed by a corresponding growth of the towns of
Montrose, Delta and Olathe.
WRITTEN ESPECIALLY FOR THE MENTOR BY C. J. BLANCHARD
ILLUSTRATION FOR THE MENTOR, VOL. 6, No. 17, SERIAL No. 165
COPYRIGHT, 1918, BY THE MENTOR ASSOCIATION, INC.
[Illustration: ROOSEVELT DAM, ARIZONA]
_RECLAIMING THE DESERT_
_The Roosevelt Dam_