Argillite Boulder – Rattlesnake Mountain, Washington
This image depicts an interesting perspective of time. The rock in the foreground was deposited here on Rattlesnake Mountain around 15,000 years ago. The Rattlesnake Mountain and the Horse Heaven Hills in the background were created as part of the Yakima Fold formation about 1.5 million years ago. The bedrock of this area is basalt from basalt flows through eastern Washington from 6-15 million years ago. The argillite boulder in the foreground is metamorphic rock from western Montana formed 1.5 billion years ago.
So here I was, sitting on a rock created before life on earth existed, brought here by a humongous flood around 15 thousand years ago, deposited on mountains uplifted 1.5 million years ago, created by a series of gigantic lava flows about 2 miles thick 6-15 million years ago. And I think I am old at 67 years. As many of my Whizzy friends would say, “It’s a thinker.”
As glaciers moved southward during the Ice Ages, they scoured the terrain picking up rock debris. During the Missoula Floods, parts of the glaciers would break off forming ice bergs. These were carried down through the Eastern Washington scablands into the Pasco basin. As Lake Lewis formed, many of the ice bergs floated to the edges of the lake. As the lake emptied, several of these ice bergs were left stranded on the surrounding ridges. They melted leaving mounds of accumulated rocks, gravel, and sand. These are “bergmounds”.
Most bergmounds are found in the Pasco Basin at elevations of 600 – 850 feet. They are 20 – 35 feet higher than the surrounding terrain. The bergmound pictured above is on a plateau of eastern Rattlesnake mountain above Richland, WA. The bergmounds are somewhat inconspicuous unless, one is looking for them.
Granite Erratic – Rattlesnake Mountain, Washington
The Missoula Floods carried large icebergs from the glaciers that dammed Lake Missoula or from the Okanagan lobe glacier that dammed Lake Columbia along with them as they made their way to the Pacific. As the icebergs melted or became “stranded” against ridges that formed Lake Lewis, they dropped the rocks that the glaciers picked up as they scoured their paths southward. Granite is present in Montana as well as northern Washington. But it is not present in central Washington. The origin of this single granite erratic on Rattlesnake Mountain is therefore not definite. It could have come from either Montana or northern Washington.
This chunk of granite is approximately 6′ in length. It is located at about 800 feet elevation (my estimate).
Sentinel Gap Looking South from Frenchman’s Spring Coulee
This image was taken from the bottom of Frenchman’s Spring Coulee near where it enters the Columbia River. Sentinel Gap was cut across the Saddle Mountains by the Columbia River and the Ice Age Floods. During the floods, the Columbia River was at a level near the top of the eastern slope of the Gap. On the north side of the Gap, the Vantage Bridge and Wanapum Dam are faintly visible. Through the Gap, Umatilla and Rattlesnake Ridges are visible. And of course, the clouds make the image.
Rattlesnake Ridge and Pasco Basin from Saddle Mountain, Washington
This image was taken from the top of Saddle Mountain looking southwest toward Rattlesnake Ridge. During the Missoula Floods, the water level of Lake Lewis between these two ridges was about 600 feet above the current basin floor.
As I was photographing on top of the mountain, I felt a cold wind pick up. The skies turned dark and I could see the rain coming toward me. I decided it was a good time to pack up my gear and head down the steep gravel/dirt road before it turned to mud. It was the end of a good day and a great trip driving around the Pasco basin exploring for traces of the Ice Age floods.