compiled by Bennye Rushton (around 1973)
What event was responsible for the actual formation of Soap Lake? The ice age created our lake. But in order to tell it like it really was, you have to understand the events which lead up to why Soap Lake is one of a kind.
By the time the last lobes of glacial ice actually reached down into what is now Washington about 13,000 years ago, the great Columbia River had cut a channel for itself from northeast to southwest across our state, having been pushed from its original bed into low-lying areas around the lava flows as they spread across the land.
Suddenly this enormous river experienced its first dam one made of ice cutting off the flow of water near the site of Grand Coulee Dam.
For a time the water backed up into a huge lake, but the pressure soon forced an overflow and the torrents of water sought the lowest and weakest places in the terrain for their routes.
Again, the ancient river was forced to cut a new route, this time along what is now the Grand Coulee. A narrow gorge cut earlier by glacial run-off streams invited the rushing water toward the lake that covered what is now the Quincy flats. There the water slowed and deposited its heavy load of silt and gravel before rejoining its old bed near Crescent Bar.
Just at the site of Soap Lake there was what geologists call an anticline a hill. This anticline caused the heavy current to churn and tear at the underlying lava, digging a hole which was partially refilled with mud and gravel, and soon created a waterfall.
Many days of violent current cut the lava cliff further and further back in the direction from which the water flowed. Although the lava itself is very dense and hard, the many cracks formed while the rock cooled and the seams between the separate lava flows weakened the rock.
The waterfall which started at the Soap Lake anticline "walked" back upstream about twenty miles, leaving a series of plunge pools which are now lakes, before the water was suddenly gone as quickly as it had come.
When the ice dam broke or was pushed away, and the water of the Columbia reverted back into its old riverbed. The site of this final waterfall is appropriately named “Dry Falls” and is unrivaled by other geological remains as the site of the once greatest falls in the world.
Picture of Dry Falls near Soap Lake, WA as it is now by © Judith Tramayne.
Soap Lake marks the lower, or southern end of lower Grand Coulee, and Dry Falls marks the head of it.
But, as we know, the earth is never finished changing. Nature took its course and this little fresh water glacial lake with no outlet began to change after a few thousand years of receiving ground water seepage from the surrounding higher lava flows.
The volume of water in the lake stabilized by evaporation, but the many minerals in the lava were leached southward with the flow of ground water. At one time several of the lakes in the lower coulee had a high mineral content, but eventually because of its location at the lower end of the coulee, Soap Lake out did all the others.
At the time of the first known chemical analysis, the water contained 17 minerals.