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.