Idaho
Idaho
This viewpoint along Idaho State Route 200, about one mile west of Hope, Idaho, offers a direct view of the terrain where the Cordilleran Ice Sheet's Purcell Trench Lobe blocked the Clark Fork River and created the ice dam responsible for...
This viewpoint along Idaho State Route 200, about one mile west of Hope, Idaho, offers a direct view of the terrain where the Cordilleran Ice Sheet's Purcell Trench Lobe blocked the Clark Fork River and created the ice dam responsible for Glacial Lake Missoula. The view encompasses the narrow valley where a wall of glacial ice up to 4,000 feet thick sealed the river, impounding 500 cubic miles of water across 3,000 square miles of western Montana. When you stand at this pullout, you are looking at the most consequential chokepoint in the Ice Age Floods story: every megaflood that carved the Channeled Scablands, created Dry Falls, and deposited sediment on the Pacific continental shelf began with the failure of an ice dam visible from this vantage point. The surrounding terrain shows evidence of both glacial advance -- till deposits, striations, polished bedrock -- and catastrophic flooding. Interpretive signage at the pullout explains the dynamics of ice damming and failure. This is the trigger point for the largest floods in Earth's documented history, and you can see the stage from right here.
The Green Monarch Ridge viewpoint is a large highway pullout on Idaho State Route 200 about one mile west of Hope, Idaho, and 15 miles east of Sandpoint. No facilities beyond the pullout; year-round access weather permitting. Free.
This is arguably the single most important interpretive viewpoint on the entire Ice Age Floods Trail. The Purcell Trench lobe of the Cordilleran Ice Sheet, advancing south from British Columbia, was stopped against Green Monarch Ridge on the east side of the present Lake Pend Oreille basin. The lobe built an ice dam estimated at up to 4,000 ft tall and nearly 40 miles wide that blocked the Clark Fork River, impounding Glacial Lake Missoula to a maximum depth of about 2,000 ft over 3,000 square miles. When the dam failed, repeatedly, across the 18.2–14 ka window, roughly 600 cubic miles of water surged south and west through Lake Pend Oreille toward the Rathdrum Prairie. From the viewpoint, the ridge crest and the trench-basin geometry of the dam location are directly visible.
The chronology of dam failures has been most recently constrained by Balbas et al. 2017, which identified an early western-route flood at 18.2 ± 1.5 ka, with the Okanogan lobe blocking later flows and the last Missoula floods at 14.7 ± 1.2 ka. No updates found since 2017.
Within the Lake Pend Oreille chapter's territory; the chapter has worked toward improving interpretation at this viewpoint.
Year-round; clear days are essential to read the geometry. Combine with Farragut State Park (the breakout side) for a full-loop interpretation.
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.
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