How the Ice Age Floods shaped Washington state

Much of Washington’s dramatic landscape was shaped by some of the largest floods ever recorded on Earth. Thousands of years ago, repeated catastrophic floods (known as the Ice Age Floods or Missoula Floods), swept across eastern and central Washington, carving coulees, cliffs and wide valleys that still define the regions today. 

The Ice Age Floods in Washington 

Near the end of the last Ice Age, enormous ice dams repeatedly formed and failed in what is now western Montana. Each failure released large amounts of water that swept across eastern Washington, scouring basalt bedrock, transporting massive boulders and creating iconic landforms such as the Columbia River Gorge, Grand Coulee and the channeled scablands.  

These floods didn’t just happen once. They occurred many times, leaving behind clear geological evidence that connects landscapes across the state. 

Visualizing Washington’s flood-shaped landscape 

Because the scale of the Ice Age Floods is difficult to imagine, the National Park Service created a 3-minute animated video that shows how floodwaters moved across Washington and beyond. The animation highlights how sites across the state are part of a connected geological system, helping viewers see familiar places in new ways. 

The animation was developed by the National Park Service in collaboration with scientists, educators and regional partners with expertise in Ice Age Floods research.  

State parks impacted by the Ice Age Floods 

You can trace the path from the Ice Age floodwaters from ancient glacial Lake Missoula to the Pacific Ocean by visiting state parks across Washington. More than a dozen state parks are located along the path of the Ice Age Floods National Geologic Trail.  

As you explore each park, look for physical clues left behind that reveal how the Ice Age Floods helped form the landscapes we recognize today. 

From east to west, find out which parks are considered major Ice Age Flood sites: 

Riverside 

At the popular Bowl & Pitcher geological feature in Riverside State Park, careful observation reveals the presence of pillow basalt where upper lava flow came into contact with lake water, quickly solidifying on contact. The giant boulders that make up this feature likely came to their present resting place during the Ice Age Floods.  

Visiting Riverside: Observe the giant boulders that make up the Bowl & Pitcher feature from the Bowl & Pitcher Suspension Bridge, showing how the weaker clay and sand was easily washed away during the floods, removing the support for overlying rocks, which then tumbled down into their current jumbled position. 

Palouse Falls 

Palouse Falls, also known as Washington’s official state waterfall, was formed by Ice Age Floods. The Palouse River runs through a narrow canyon and drops 200 feet at Palouse Falls into a churning bowl. From there, the water current moves swiftly through a deep and winding gorge cut through several layers of basalt lava flows, eventually joining the Snake River, which is a major tributary of the Columbia River.  

Visiting Palouse Falls: If you’ve ever been to Palouse Falls, you know how iconic it is. Those who have not visited yet can use the multiple overlooks and interpretive signage to help paint the picture of how the region came to be. 

Steamboat Rock 

Geologists have catalogued evidence that Steamboat Rock was formed during the Ice Age Floods, when churning water scoured the land surrounding the butte and streamed over its top. The rock is thought to be the remnants of the upper falls of the Grand Coulee, a massive twin waterfall twice the height of Dry Falls.  

Visiting Steamboat Rock: The day-use provides panoramic vistas views of Steamboat Rock flanked by Banks Lake and outcrops of granite also shaped by the floods. 

Sun Lakes-Dry Falls 

Sun Lakes-Dry Falls preserves one of the most dramatic landscapes shaped by the Ice Age Floods. During repeated flood events, enormous volumes of water poured through the Grand Coulee, creating a waterfall estimated to be four times wider than Niagara Falls. As floodwaters scoured the basalt bedrock, they carved deep channels that later fill with water, forming the park’s lakes. 

Visiting Sun Lakes-Dry Falls: If you’ve ever visited this park, you can see the striking evidence of Ice Age Floods through the towering cliffs, dry plunge pools and surrounding scablands. Stand at the overlook or take a peek inside the Dry Falls Visitor Center for more information on how the Ice Age Floods affected the Coulee Corridor.  

Ginkgo Petrified Forest 

Ginkgo sits along the Columbia River, which carried enormous floodwaters during the Ice Age Flood events. Pooled waters from the floods deposited large floating icebergs, some carrying clusters of erratic rocks from far away. 

Visiting Ginkgo: Visit the Ginkgo Petrified Forest Interpretive Center to get a more in-depth experience on how the Ice Age Floods affected Vantage, Washington. 

Columbia Hills 

Spires and buttes such as Horsethief Butte were eroded by a series of glacial lake outburst floods that blasted through the Columbia River Gorge, leaving behind the stark rock walls. 

Visiting Columbia Hills: Along the Horsethief Butte Trail, you’ll find interpretive signage about the Ice Age Floods at the trailhead near the rock’s base, and more at its summit.  

Beacon Rock 

Rushing water, mud and ice raced through the Columbia River Gorge at speeds up to 60 miles-per-hour. The force of the floods stripped away tons of soil and rock, including everything but the hard core of the Beacon Rock cinder cone.  

Visiting Beacon Rock: For thousands of years this rock has been seen and appreciated. It is far from a “Boring” volcanic lava flow. Come walk up the 845-foot ancient volcanic core and get incredible views of the Columbia River Gorge. 

Cape Disappointment 

Cape Disappointment sits on a high bluff overlooking the Columbia River and the Pacific Ocean, providing the perfect vantage point to observe where the Ice Age Floods traveled all the way to the Pacific Ocean.  

Visiting Cape Disappointment: Cape Disappointment’s Lewis and Clark Interpretive Center, provides visitors with a visual representation of the catastrophic floods. 

Additionally, Mount Spokane, Lyons Ferry, Crown Point Heritage Site, Sacajawea, Potholes, Lake Lenore Caves, Bridgeport, Daroga, Lincoln Rock, Wenatchee Confluence and Maryhill are all considered secondary Ice Age flood sites. 

From towering basalt buttes to winding river gorges to coastal bluffs, the story of the Ice Age Floods is written across Washington’s landscape. What started as a catastrophic release of glacial water thousands of years ago, now defines some of Washington’s most recognizable state parks.  

The next time you visit a Washington state park, take a closer look at the cliffs, coulees and riverbeds around you. You may be standing in the path of one of the largest floods ever known.