Ice Age Floods National Geologic Trail
Ice Age Floods National Geologic Trail
Cabinet Gorge Dam on the Clark Fork River sits near the single most consequential location in the entire Ice Age Floods story: the approximate site of the ice dam that created Glacial Lake Missoula. The Purcell Trench Lobe of the Cordilleran Ice Sheet advanced down this valley...
Cabinet Gorge Dam on the Clark Fork River sits near the single most consequential location in the entire Ice Age Floods story: the approximate site of the ice dam that created Glacial Lake Missoula. The Purcell Trench Lobe of the Cordilleran Ice Sheet advanced down this valley and blocked the Clark Fork River near what is now the Idaho-Montana border, impounding a lake that grew to hold 500 cubic miles of water across 3,000 square miles of western Montana. When the ice dam failed -- an event that may have occurred 40 or more times over 2,500 years -- the lake's entire contents emptied through this narrow gorge in as little as 48 hours, producing the largest floods known to have occurred on Earth. Core samples taken during the dam's construction revealed multiple stages of ice damming and flooding, confirming the repeated catastrophic cycle. An AVISTA-maintained viewpoint at the dam includes Ice Age Floods interpretive signage and offers an excellent vantage point for pondering the most important question in flood geology: how exactly did an ice dam 2,000 feet thick fail catastrophically? Stand here and you stand at the trigger of the largest floods in Earth's history.
Cabinet Gorge Dam straddles the Idaho–Montana state line on the Clark Fork River, just east of Clark Fork, Idaho. The dam (Avista Utilities, 230 MW) is operational. A public overlook is accessible from a marked turnoff on Idaho Highway 200 east of Clark Fork. The overlook is free, open year-round, and best in spring during snowmelt high flows. The Cabinet Gorge Fish Hatchery (downstream) offers tours by arrangement.
Cabinet Gorge sits at the eastern end of the constriction where the Purcell Trench Lobe of the Cordilleran Ice Sheet repeatedly advanced south and west to dam the Clark Fork River, ponding Glacial Lake Missoula. Cores taken during the dam's construction in the 1950s revealed multiple stages of ice-dammed lake sediment and till, consistent with at least several dam-and-flood cycles at this exact location. The ice plug here typically rose around 2,000 feet (some estimates to 4,000 feet); when it failed, the entire impounded volume of Lake Missoula released through this gorge as the head of every Missoula flood. The narrowness of Cabinet Gorge is itself a flood-relevant feature: the constriction concentrated the discharge that subsequently spread across the Rathdrum Prairie and Channeled Scabland.
Roy Breckenridge's "Mapping the Deluge: Sandpoint to Cabinet Gorge Dam" (Idaho Geological Survey Staff Report S-14-1) remains the field-trip standard. No new outburst-mechanism papers specifically targeting Cabinet Gorge since 2017; Balbas et al. (2017) sets the broader chronology at ~18.2 ± 1.5 ka for the largest flood and ~14.0–14.4 ka for the youngest.
Strong. The IAFI Coeur du Deluge Chapter (Sandpoint) leads field trips along Highway 200 between Sandpoint and Cabinet Gorge, including boat trips up the Clark Fork River Delta to the historic dam location. The chapter is the most active interpretive presence for this segment of the trail.
Best May–June at peak runoff for dramatic flow over the spillway. Allow 30–60 minutes at the overlook. Pair with the Clark Fork Ice Dam site immediately west and the Lake Pend Oreille shoreline.
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.