A strong dam depends not just upon the concrete you see, but on the unseen structure beneath river level. During construction, engineers drilling to find bedrock encountered deep, unstable deposits of glacial silt - loose gravel and sand. Water kept seeping through and undermining diversion dams built to allow excavation. To solve the problem, the crews inserted a network of refrigeration tubes into the till and created a giant ice plug, freezing the gravel in place so that excavation could continue.
Completed in 1961, the 300-foot-high (90-meter) dam is set down into bedrock. It extends an almost equal distance above the river bed and down into the thick layer of gravel and sand between river and rock. Glaciation and other processes that shaped this gorge over the past million years have proved expensive challenges to dam-building.

Sorry, but we don't have a picture of this historical marker yet. If you have a picture, please share it with us. It's simple to do. 1) Become a member. 2) Adopt this historical marker listing. 3) Upload the picture.

Show me all markers in:  Rockport, WA  |  Whatcom County  |  98283  |  Washington  |  United States of America

Transmission Lines
Chain of Dams
Lighting of the Falls
Electric Forest
Welcome to Ladder Creek Falls & Gardens
Gorge Powerhouse
The North Cascades
A Park From the People
Concrete Bank Building
Safety Follows Wisdom

• GPX
• KML
• LOC

Have you seen this marker? If so, check in and tell us about it.