The word Tumwater is a mixture of Chinook and English. Tum comes from Tumtum, which means heartbeat. People thought that the sound of the water falling was like a heartbeat. What an appropriate place for a cache, at the biggest waterfall on the Tumwater (albeit manmade).
Tumwater Dam was completed in 1909, to create electricity to power the electric locomotives that pulled trains through the nearby Cascade Tunnel. Before the dam was built, the people in the trains going through the tunnel would suffer from smoke and fumes build up. People became sickened from traveling through the tunnel until they were able to use the electric locomotives.
Today, a fish ladder provides access for salmon and trout to move upriver. If you have the time, walk down the stairs and enjoy the view of the beautiful waterfall created by the dam.