Ice Age Floods National Geologic Trail
Ice Age Floods National Geologic Trail
Summer Falls is a living waterfall born from the Ice Age Floods, cascading over basalt ledges in the upper Grand Coulee at the edge of Billy Clapp Lake. While not as massive as the ancient Dry Falls downstream, Summer Falls is actively flowing and offers an intimate encounter...
Summer Falls is a living waterfall born from the Ice Age Floods, cascading over basalt ledges in the upper Grand Coulee at the edge of Billy Clapp Lake. While not as massive as the ancient Dry Falls downstream, Summer Falls is actively flowing and offers an intimate encounter with the same basalt formations that the megafloods carved on a much grander scale. The falls exist because the floods eroded away softer rock layers and fractured the basalt along columnar jointing planes, creating the step-like ledges that the water now cascades over. The surrounding landscape of scabland channels, pothole lakes, and basalt outcrops preserves the raw texture of the flood-carved terrain. In spring, when snowmelt and irrigation flows boost the water volume, the falls provide a small taste of the immense power that once thundered through this coulee. The park is a compact, scenic stop that rewards a short visit with waterfall views and a direct connection to the flood geology. It makes an excellent companion stop to Dry Falls, just a short drive down the coulee, offering flowing water where Dry Falls offers only the memory of it.
Summer Falls is a small day-use state park about 9 miles southwest of Coulee City, Washington, in the Lower Grand Coulee. It is open seasonally roughly April 1 to September 30, 6:30 a.m. to dusk, with a winter schedule of 8 a.m. to dusk October 1 to March 31. No camping; Discover Pass required. The waterfall itself is a Bureau of Reclamation irrigation discharge, not a natural year-round flow.
Summer Falls sits at the head of Billy Clapp Lake within the Lower Grand Coulee — country directly carved by the Missoula floods. The coulee floor here is a flood-scoured basalt channel; the waterfall happens to plunge over an exposure of the same Columbia River Basalt that formed the cataract face at Dry Falls a few miles upstream. The 165-foot drop today is artificial in origin (water from Banks Lake via the Main Canal of the Columbia Basin Project), but the cliff and the channel below are pure flood geology. During the largest floods, water filled the entire coulee well above today's falls, with Upper and Lower Grand Coulee acting as a single deep flood passage at depths estimated in the hundreds of feet.
No site-specific publications located. Cosmogenic dating of Upper and Lower Grand Coulee flood pulses (Balbas et al. 2017; USGS review O'Connor and Baker 2020) places the largest floods at roughly 18.2 ka with continued reactivation through about 14.0 ka.
The Lower Grand Coulee Chapter (Soap Lake/Ephrata) covers this stretch. No dedicated on-site IAFI panel located.
Late spring through early fall, while the Reclamation canal is delivering water and the falls are flowing — outside that window, the falls are essentially dry. Combine with Dry Falls and Lake Lenore Caves for a Lower Grand Coulee loop.
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.