The Tieton Dam is an example of remarkable engineering. The project was started in 1917 and although the sounds of construction were faint during the war years, the loud echoes of men at work were welcome during the depression that followed. The little town at the base of the dam flourished and faded, reflecting the activity at the dam site. The miners that excavated tons of earth and rock fill, the laborers that poured concrete, built railroad scaffolding and carved timbers, the loggers, muleskinners and engineers all resided at the town of Rimrock while there was work to be found. The general store capitalized on the late snows in the mountains and the cattle grazing in the high meadows to produce ice cream a favorite treat for all members of the community.
Teams of mules pulled heavy sleds loaded with this 14 ton locomotive from the town of Naches to the construction site of the dam. Once there, it traversed the Tieton Canyon suspended on a cable to settle on the narrow gage track prepared for its arrival. Evidence of the cable holds can still be found in the rocks above each side of the dam. This locomotive traveled backward and forward, pushing and pulling side dump railcars, transporting the fill material that surrounds the concrete core of the dam. The concrete core extends 100 feet below the original riverbed and the bottom of the dam.
In 1925, Tieton Dam was the largest earthfill dam in the world. The side dump railcars had dropped 2,049,000 cubic yards of earth down the sides of the concrete core. In this process, the railroad track was continually buried and rebuilt as the height of the dam increased. Portions of the track can still be seen when the water level in the reservoir is low.
A steady supply of lumber was needed for railroad ties, scaffolding and underground support beams. To meet this need efficiently, a mill was located near the construction project. Many of the trees used in the building of the dam were harvested from the area that is now underwater.
Dirt, seat and the echo of hammer against rock were familiar to miners of the early 1900's. These miners made a significant contribution to the construction of the Tieton Dam, Carving a tunnel through hand native basalt to complete the outlet channel under the dam. a measure of the task is illustrated by the Highway 12 tunnel on half mile east of the site which was excavated through the same material.
The outlet channel is 1800 feet long. Approximately 600 feet of that distance was forged through solid rock, leaving a tunnel that looks the same today as it did 70 years ago. This channel pipes the water from the reservoir under the dam, pas slide gates, to the valve house which controls the amount of water leaving the reservoir.
Today the dam hides new technology beneath an exterior that shows little evidence of change. Construction began in 1917 and was completed in 1925. The gates and valves in the outlet channel were updated in 1989. The wedge shaped structure measures 40 feet in the width at the crest and 1,100 feet at the base. It is 319 feet high. Behind the dam is Rimrock Lake, a reservoir holding 198,000 acre feet of water at full capacity. Rimrock Lake was left as a tribute to future residents of the Yakima Valley from the people that anticipated the agricultural potential of the Valley below the dam. This reservoir was the first step toward assuring a supply of water for the developing agricultural economy. Now this system supports thousands of acres of fruit and vegetable crop land.
In recent years, the reservoir has grown increasingly more popular as a recreation site. Traditional activities such as boating and water skiing having been supplemented by windsurfing and white water rafting. Trail systems that accommodate the hiker and horseman have expanded to include the snow mobiler, mountain biker and cross country skier. A road system around Rimrock Lake provides opportunities for those who enjoy a leisurely, scenic drive on a paved surface. This area around Rimrock Lake has uniquely responded to diverse recreation demands. Those that worked on the dam and their families have given way to fishermen, hikers, hunters and campers, attracted by countless recreation opportunities, majestic scenery and visions of the past.
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