Washington
Washington
At the confluence of the Snake and Columbia Rivers near Pasco, Sacajawea State Park occupies a spot that was ground zero for some of the most turbulent water dynamics during the Missoula Floods. Floodwaters pouring down both the Columbia...
At the confluence of the Snake and Columbia Rivers near Pasco, Sacajawea State Park occupies a spot that was ground zero for some of the most turbulent water dynamics during the Missoula Floods. Floodwaters pouring down both the Columbia and Snake River corridors collided here, creating a massive zone of churning whitewater before being forced through the Wallula Gap bottleneck downstream. During peak flood events, this confluence was submerged beneath Glacial Lake Lewis, which rose to 1,250 feet above sea level as water backed up behind Wallula Gap faster than it could drain through. The park's flat terrain is built on flood deposits -- enormous gravel bars and sand sheets deposited when the lake finally drained. Lewis and Clark camped near this confluence in October 1805 on their way to the Pacific, making this a place where the expedition's human story overlaps with the geological story of the floods. The park's interpretive center focuses on Sacajawea and the Corps of Discovery, but the landscape itself tells an even older story of water, ice, and unimaginable power.
267-acre day-use park at the confluence of the Snake and Columbia rivers in Pasco. Park grounds are open seasonally April 1–October 31, 8 a.m. to dusk; closed November 1–March 31. The Sacajawea Interpretive Center operates Wednesday–Sunday during the open season and by appointment in winter. Discover Pass required. The interpretive center covers the Corps of Discovery, Sacagawea, and the Sahaptin-speaking tribes; flood interpretation is a secondary thread.
The park sits squarely in the floor of Lake Lewis, the temporary lake that filled the Pasco Basin behind the Wallula Gap constriction during each Missoula Flood. Water depths here reached roughly 800 feet during the largest events. Slackwater rhythmite deposits underlie the park grounds and are exposed in cuts and bluffs in the broader Tri-Cities area. The confluence itself is a geologic crossroads: the Snake River arrives from the east carrying its own pre-Missoula gravel record, the Columbia from the north carrying flood deposits, and the combined channel exits south through Wallula Gap a few miles downstream. Visit Tri-Cities and the REACH Museum (nearby in Richland) treat the area as Lake Lewis ground zero.
Coyote Canyon Mammoth Site work (Wegener et al., 2021, in Quaternary) refined the Missoula flood chronology in the Tri-Cities area using rhythmite stratigraphy. The 2020 O'Connor et al. USGS review is the broader synthesis.
Direct IAFI Lake Lewis Chapter site. The chapter publishes the Lake Lewis Floodscape Brochure, which uses Sacajawea State Park as a key interpretive stop.
Best April–October; closed in winter. Pair with the REACH Museum in Richland (Geologic Past: Ice Age Floods gallery) and Wallula Gap downriver for a one-day Lake Lewis loop.
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