The Waterville Plateau near Sims Corner is an open-air museum of glacial landforms, preserving some of the finest eskers and kames in the Pacific Northwest. Eskers -- sinuous ridges of sand and gravel deposited by rivers flowing through...
The Waterville Plateau near Sims Corner is an open-air museum of glacial landforms, preserving some of the finest eskers and kames in the Pacific Northwest. Eskers -- sinuous ridges of sand and gravel deposited by rivers flowing through tunnels beneath the ice sheet -- snake across the plateau like frozen rivers, some stretching for miles. Kames, cone-shaped hills of debris deposited where meltwater poured through holes in the ice, dot the landscape alongside scattered glacial erratics -- boulders carried hundreds of miles from Canada and dropped here as the ice melted. These features were created by the Okanogan Lobe of the Cordilleran Ice Sheet during its retreat, and their remarkable preservation owes much to the semi-arid climate that has protected them from erosion for over 13,000 years. Together with the nearby Withrow Moraine, this site provides an extraordinary record of how a massive glacier lived and died on this plateau. The rolling wheat fields around Sims Corner hide a landscape shaped entirely by ice, and every ridge and hillock tells part of the story.
The site is a National Natural Landmark (designated 1986) on the Waterville Plateau in Douglas County, Washington, north of the towns of Mansfield and Sims Corner. It sits on a mix of public and private rangeland; there is no formal park, visitor center, or signed trail. Most viewing is from State Route 172 and adjacent county roads, visitors should respect property lines and the working-ranch setting.
Sims Corner is primarily a glacial-deposition site rather than a flood-erosion site, and that distinction matters. The eskers, kames, kettles, terminal moraines, and erratics here record stagnation of the Okanogan Lobe of the Cordilleran Ice Sheet at the southernmost extent of glaciation on the Columbia Plateau. The same ice mass that built these features also diverted the Columbia River south into Moses Coulee and later Grand Coulee, setting up the routes the Missoula Floods would exploit. Floodwaters from Glacial Lake Missoula did not directly scour the Sims Corner plateau, but the landforms preserved here are part of the same Pleistocene system. The site is included on the Ice Age Floods National Geologic Trail as a complement to the flood-erosion landscapes downslope at Moses Coulee and Grand Coulee.
No site-specific updates found since the original NNL evaluation. Regional cosmogenic-dating work on the Okanogan Lobe and the megaflood chronology (Balbas et al. 2017; Hanson et al. 2020) anchors the largest northwestern Columbia floods at roughly 18.2 ka but does not target Sims Corner directly.
No dedicated chapter, panel, or named partnership located. The Wenatchee Valley Erratics Chapter is the nearest IAFI chapter to the Waterville Plateau and occasionally references the area on regional field outings.
Late spring through early fall is the practical window, winter roads can be drifted closed, and summer heat on the plateau is severe. Plan it as a driving loop combining Sims Corner with Moses Coulee, McNeil Canyon Haystack Rocks, and Boulder Park; expect minimal interpretive signage and no services.
Three vantages no single photograph can hold, the same treatment that made Dry Falls legible.
Ground-level panoramas along the feature, so the scale of the flood landscape is something you stand inside.
An aerial reveals the geometry of catastrophe: scour, channels, and bars that are invisible at eye level.
A model of a key outcrop you can rotate and measure in the browser, the rock itself, on the page.
Capture window mid-June through mid-July 2026 · slots fill on this page as the campaign delivers.
Flood-extent overlay shows the maximum reach of the Missoula Floods.
The site in its place along the flood path, with the maximum flood extent drawn over the modern map.
View on the interactive map Cinematic timeline · 3D flood · every captured site