Boulder Park on Washington’s Waterville Plateau preserves unusually clear evidence of Ice Age glaciation and is recognized as a National Natural Landmark. Northeast of the Withrow Moraine, it occupies a broad upland basin over part of Moses Coulee, where Columbia River Basalt is partly covered by glacial deposits laid down roughly 14,000 to 20,000 years ago. Its conspicuous boulders include granodiorite and gneiss erratics carried south by the Okanogan ice lobe, as well as local basalt “haystack rocks” torn from bedrock by the glacier. Together these features reveal the power and direction of glacial movement and help document classic Pleistocene ice-stagnation landforms in Washington.