Sims Corner Eskers and Kames, on the Waterville Plateau in north central Washington, preserves unusually clear Pleistocene glacial features such as eskers, kames, terminal moraines, and glacial erratics, earning recognition as a National Natural Landmark. The area rests on the Columbia River Basalt Group, formed by massive Miocene flood-basalt eruptions and later exposed by erosion and the Missoula Floods. Its most important landforms were created much later as glaciers advanced, stagnated, and melted across the plateau. This glacial activity, tied to the Okanogan lobe’s blockage of the ancient Columbia River, helped redirect regional drainage and contributed to the carving of Foster Coulee, Moses Coulee, and the modern Grand Coulee.