Ice Age Floods National Geologic Trail
Ice Age Floods National Geologic Trail
Bonneville Dam, completed in 1938 as the first federal dam on the Columbia River, would have been utterly invisible beneath the Missoula Floods -- submerged under hundreds of feet of churning floodwater that dwarfed this massive structure the way an ocean wave dwarfs a...
Bonneville Dam, completed in 1938 as the first federal dam on the Columbia River, would have been utterly invisible beneath the Missoula Floods -- submerged under hundreds of feet of churning floodwater that dwarfed this massive structure the way an ocean wave dwarfs a sandcastle. During peak flood events, the water level at this location exceeded 800 feet above sea level, compared to the dam's crest at around 100 feet -- meaning the floodwaters were stacked seven times higher than the dam itself. The Columbia Gorge at Bonneville was one of the most constricted sections of the flood path, concentrating the flow and accelerating it to enormous velocities. The Visitor Center offers exhibits on hydroelectric power and the Columbia River's salmon runs, but the geological setting tells an even more powerful story. The surrounding canyon walls show scour marks and polished surfaces far above the modern river, and the gorge's characteristic waterfalls -- including Multnomah Falls just upstream -- exist because the floods deepened the canyon and steepened its walls. Bonneville Dam is an engineering marvel; the floods that preceded it were a natural force beyond any engineering.
The Army Corps of Engineers operates two visitor centers — Bradford Island (Oregon side, off I-84) and Washington Shore (off SR-14). Both are open 9 a.m. to 5 p.m. daily, 362 days a year (closed Thanksgiving, Christmas, New Year's Day). Admission is free. Public tours are offered intermittently as staffing allows; reservations via (541) 374-8820.
The dam site sits at the head of the Columbia Gorge's narrowest reach and is roughly at river level — the same corridor through which every Missoula flood thundered toward the Pacific at speeds approaching 60 mph and depths of hundreds of feet. The Cascades Rapids that the dam now drowns were created not by the Missoula floods but by the ~1450 CE Bonneville Landslide off Table Mountain, which dammed the Columbia and was later breached. Treat this stop as a Gorge geology vantage point: the floods are part of the area's story, but the visitor center exhibits are weighted toward dam operations, fish ladders, and salmon, not flood interpretation. Best opportunity to see migrating salmon is late April through early November.
No updates found since the O'Connor et al. (2020) Missoula and Bonneville floods USGS review. Balbas et al. (2017) remains the chronology anchor at ~18.2 ± 1.5 ka for the largest floods.
The IAFI Columbia River Gorge Chapter (founded 2007) is the responsible chapter and has held programs at the Columbia Gorge Interpretive Center and Discovery Center, both nearby. No dedicated IAFI page for the Bonneville Dam Visitor Center is published; no IAFI-installed panel at the dam is documented.
Year-round visit; fish-ladder viewing peaks August–October for Chinook and steelhead. Best paired with Beacon Rock, the Columbia Gorge Interpretive Center (Stevenson, 7 miles east), and Multnomah Falls.
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.