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Penstock Bridge

This riveted steel Baltimore Petit truss was built in 1909 by the Great Northern Railroad Company as part of the Tumwater Hydroelectric Plant. The hydroelectric installation, which was an extensive system that required conductors and additional power stations, was built to power the Great Northern trains over a 57-mile mountain division from Leavenworth to Skykomish. The water, which was the power source for the electrification of the tunnel, was transported approximately two miles by a penstock from a 250-acre storage site to the powerhouse. The seven-panel bridge was constructed to carry the 8.5-foot-diameter penstock from the south bank of the river to a surge tank at the corner of the powerhouse. Most of the penstock was wood stave pipe; however, the last 952 feet of pipe, part of which passed through the bridge, was constructed of riveted steel. The penstock pipe through the bridge has been cut, to enable the bridge to be used as a pedestrian walkway. The bridge is one of the early examples of a riveted steel Baltimore Petit truss and remains as one of the few extant reminders of the early attempts to electrify the railroads through the Cascade Mountains.