Ice Age Floods National Geologic Trail
Ice Age Floods National Geologic Trail
This quiet confluence of two rivers hides one of the most startling discoveries in geological history: proof that the mighty Snake River once ran backward. When J Harlen Bretz explored this area in the 1920s, he found enormous gravel bars -- some towering 100 feet above the...
This quiet confluence of two rivers hides one of the most startling discoveries in geological history: proof that the mighty Snake River once ran backward. When J Harlen Bretz explored this area in the 1920s, he found enormous gravel bars -- some towering 100 feet above the river -- deposited in a pattern that could only mean floodwaters had reversed the Snake River's flow, pushing water eastward up the valley for miles. These giant bars, composed of house-sized boulders and gravels tumbled at highway speeds, were among the first hard evidence supporting Bretz's then-heretical theory that catastrophic floods, not gradual erosion, had carved the Channeled Scablands. Today the area around Lyons Ferry State Park preserves this dramatic flood-carved terrain where multiple scabland flood paths converged, funneling water from across eastern Washington into the Snake River corridor before it continued westward to Wallula Gap. The layered gravels visible in the riverbanks here record not one but dozens of separate megaflood events, each one powerful enough to reverse a major river.
The confluence sits at Lyons Ferry, where Lyons Ferry Marina and the adjacent Washington State Parks day-use area (formerly Lyons Ferry State Park) provide access. The state-park land was transferred to the Confederated Tribes of the Colville Reservation and is operated as a day-use site; the marina is privately operated. A Discover Pass is required at the state-managed portion. Open year-round; basic facilities and limited parking.
This is where the diverted Palouse River exits its flood-carved canyon and joins the Snake. The Missoula floods backed up here as Lake Lewis filled the Pasco Basin behind the Wallula Gap constriction, depositing the Lyons Ferry gravel bar — an immense flood-built bar with the stratigraphic signature of high-energy basaltic-pebble flood gravels overlain by quieter slackwater rhythmites. Pre-Missoula flood deposits are also documented along this reach. The site is a key stop for understanding the diversion of the Palouse drainage and the lower-energy ponded conditions that produced the rhythmites.
Documented in Bjornstad and Kiver's On the Trail of the Ice Age Floods (Snake River chapter) and in O'Connor et al.'s 2020 USGS review. The Ice Age Floods Explorer (floodexplorer.org) catalogs the gravel bar as Item 23. No new site-specific peer-reviewed work since.
Site falls within both the IAFI Palouse Falls Chapter and the IAFI Lake Lewis Chapter coverage areas; both run field trips through this confluence.
Best in spring and early summer when flows are highest; access roads can be hot and exposed in midsummer. Pair with a stop at Palouse Falls upstream — same drainage, complementary stories.
Every site along the trail will receive the full Terrain360 capture treatment: ground-level 360° panoramas, drone aerial imagery, and photogrammetry-based 3D models that visitors can spin in their browser. This page reserves the slots; the imagery flows in as field capture completes.
Ground-level 360° panorama, every step along the feature, captured by Terrain360 field crews.
Drone flyovers reveal the geometry of catastrophe — ripple marks, gravel bars, and scour patterns invisible from the ground.
Photogrammetry and Gaussian-splat models let visitors rotate, measure, and inspect features in detail-page WebGL viewers.