Penstock Bridge was built as one of several partial solutions to the problems inherent in building and operating a railway across a rugged mountain range. The original route of the Great Northern Railway traversed the Cascades at Stevens Pass on thirteen miles of switchbacks covering a straight line distance of three miles. It took over an hour to complete the journey in the best of circumstances. The trains could be delayed for days when winter storms piled snow twenty feet deep along the tracks.
The three mile long Cascade Tunnel opened in 1909 eliminating the switchbacks however a new set of unforeseen problems arose. The life of more than one railroader was lost as temperatures soared and carbon monoxide laden engine exhaust built up in the unventilated shaft. Only the alert action of a crewman, who was riding with the passengers, saved the one hundred people on board a train that stopped for an extended time in the tunnel. He noticed a great number of the travelers dozing off, realized the cause and released the handbrakes. The cars rolled out of the abyss and into the fresh air in the nick of time. The ensuing public outrage in the wake this 1903 incident forced the railroad to come up cure for the frightful conditions in the tunnel.
Completion of the Tumwater Canyon hydroelectric project, near Leavenworth, Washington
allowed the railway to switch from steam to electric powered engines in 1909 fixing the exhaust fume problem in the tunnel. Construction began in 1907. The canyon’s geography dictated the location of the powerhouse on the west bank of the Wenatchee River two miles below the dam. Penstock Bridge was constructed in 1907 to serve as an access for crews working on the powerhouse and to latter carry the four foot diameter pipe, i.e. the penstock, that would carry water from the dam to the turbines.
The electrification project succeeded in solving only one of the problems with the Cascade Tunnel route. A 1910 avalanche just east of the tunnel entrance took the lives of ninety passengers on an unlucky train. A new public outcry forced construction of a new Cascade Tunnel. This one is nearly eight miles in length and was not completed until 1929. A modern ventilation system was installed in the new tunnel in 1956, allowing the railroad to switch from electric to diesel locomotives at this time the Chelan County Public Utility District acquired the dam and generating facility. The PUD installed fish ladders at the dam and removed the powerhouse and penstock as a fishery restoration project. The bridge remains and is open to foot traffic. Its deck is a half section of the old riveted penstock pipe lined with sand.