Boulder Park National Natural Landmark, along with the nearby McNeil Canyon Haystack Rocks and Sims Corner Eskers and Kames natural landmarks, illustrate well-preserved examples of classic Pleistocene ice stagnation landforms that are found in Washington. These landforms include numerous glacial erratics and haystack rocks that occur near and on the Withrow Moraine, which is the terminal moraine of the Okanogan ice lobe.GeomorphologyBoulder Park is located on the Waterville Plateau of the Columbia Plateau in north central Washington state in the United States. It is a broad, dish-shaped upland basin that that overall dips gently northward. The Waterville Plateau extends east from Columbia River to the Grand Coulee. This plateau is underlain by Columbia River Basalt that is covered by a discontinuous blanket of 14,000 to 20,000 year-old glacial deposits.This park lies about 6km northeast and 17km north of the arcuate ridge of the Withrow Moraine. It marks the southern, 17,000 year-old terminus of the Okanogan ice lobe and southern margin of the Cordilleran Ice Sheet. Boulder Park and adjacent areas is covered by a discontinuous blanket of gravelly, sandy loam glacial till. These glacial deposits overlie and partially to completely fill Moses Coulee, a paleochannel cut by a pre-Wisconsin, megaflloods that predate the Last Glacial Maximum. It was cut by older Spokane Floods at a time prior to when the Okanogan ice lobe partially covered the Waterville Plateau during most of the last of the Last Glacial Maximum. At its maximum extent, this ice lobe was up to 300m thick and 40km wide. It effectively blocked most of the Columbia River Valley and created Glacial Lake Columbia.
