The Priest Rapids Bar is one of the most massive Ice Age Floods gravel bars in existence -- a mountain of flood debris rising over 400 feet above the Columbia River and covering an enormous area south of the Saddle Mountains. To put its...
The Priest Rapids Bar is one of the most massive Ice Age Floods gravel bars in existence -- a mountain of flood debris rising over 400 feet above the Columbia River and covering an enormous area south of the Saddle Mountains. To put its scale in perspective, this single gravel bar is taller than a 40-story building and contains enough material to bury a small city. The bar was deposited when floodwaters decelerated after passing through gaps in the Saddle Mountains, dropping their massive sediment load of boulders, cobbles, and gravel in a sprawling fan-shaped deposit. The size of the boulders within the bar -- some weighing many tons -- indicates the extraordinary velocity and carrying capacity of the floodwaters that transported them. The bar is best viewed from the pullout along the highway, where its sheer scale becomes apparent against the backdrop of the Columbia River below. Gravel bars of this magnitude are found nowhere else on Earth outside the Ice Age Floods region, and the Priest Rapids Bar is among the largest of them all. It is perhaps the single most impressive piece of evidence for the floods' raw sediment-moving power.
The bar itself is on Wahluke Slope (east bank of the Columbia between Vernita Bridge and Sentinel Gap) and is largely on the Hanford Reach National Monument; vehicular access is limited. The best public viewpoints are pullouts on State Route 24 descending from the Wahluke Slope, and from the Vernita Bridge area on SR 24 / SR 243. No fees; daylight hours only on monument land.
Priest Rapids Bar (also called Wahluke Bar or Mattawa Bar) is one of the largest expansion bars left by the Missoula floods. As flood pulses surged south through Sentinel Gap and Frenchman Hills, the flow expanded into the Pasco Basin and dropped its bedload. The bar surface stands roughly 430 ft above the modern Columbia, and the gravel package contains boulders up to ~1.4 m in diameter. Bar elevation and stratigraphy mark the lower bound on flood depth through this reach (Lake Lewis was deeper still upstream behind Wallula Gap). The bar surface also carries flood-current bedforms visible on lidar.
No Priest Rapids Bar–specific dating studies have been published since the Balbas et al. (2017) chronology, which dates the largest flood through this reach at 18.2 ± 1.5 ka.
The IAFI Lake Lewis Chapter covers this stretch in its Lake Lewis Floodscape brochure. No on-site IAFI signage at the bar itself.
Best in late spring or fall when haze is low. The Wahluke Slope pullouts give a long view down-bar; combine with the Wanapum Vista pullout to the north and the White Bluffs Overlook to the south for a half-day Lake Lewis geology loop.
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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