Ice Age Floods National Geologic Trail
Montana · Idaho · Washington · Oregon

The largest floods in Earth’s history.

For four thousand years, walls of water taller than skyscrapers tore the Pacific Northwest down to bedrock. This is the public home of the trail that follows them, built on the science of the Ice Age Floods Institute, with immersive 360° capture so you can stand inside the story from anywhere.

Explore the map → Walk a site in 360°
Dry Falls, WA · 360° capture · Terrain360
When the dam broke

A wall of ice two thousand feet tall held back a lake the size of Lake Erie. When it failed, the lake emptied in two days.

The water came off the ice front moving sixty-five miles an hour, carrying icebergs the size of houses and boulders the size of cars. It scoured a quarter of Washington State to rock, dug canyons in a week, and stranded granite from Montana on hilltops in Oregon. Then the ice closed the gap, the lake refilled, and it happened again. Dozens of times.

500 mi³water per flood
10×every river on Earth, combined
48 hrsto drain a lake the size of Erie
The interpretive layer

A flood you can’t see needs a way to be read.

The catastrophe ended fourteen thousand years ago. What it left is quiet, a dry coulee, a lake in a pit, a boulder in a field. Interpretation is the work of putting the water back: of standing you in the place and telling you what you’re looking at.

Every captured site carries four ways in. Walk through one and see how it works.

Open the interpretive site →
01 · NARRATIVE
The place’s story, told plainly

What happened here and why it matters, in language anyone can follow, woven around the imagery, not buried under it.

02 · LAYERED 360°
The view explains itself

Annotations placed inside the panorama. Touch a feature and the ground tells you what it is.

03 · DRONE REVEAL
What only the air can show

Top-down flood geometry, the full cataract, the channels, the staircase of pools. The June capture flies this.

04 · THEN & NOW
Fill the valley back up

Drag between the flood at its peak and the dry ground today. The reconstruction is the lesson.

Featured site
500 scenes · 360° captured
SITE 01 · DRY FALLS, WA

Umatilla Rock & the floor of Dry Falls

Once the largest waterfall on Earth, now a dry basalt amphitheater. The fully interpreted showcase, all four ways in.

Walk the site →
Explore the trail

Four ways to walk in.

Sites10

Deep interpretive profiles of every captured place.

Erratics~400

Boulders the floods rafted hundreds of miles on ice.

Field Notes1,857

Bretz’s own field record, site by site.

Peoples

The water crossed homelands. Their accounts, their words.

The science

18,200 years ago. Not “fifteen thousand.”

Most signs along the trail still say 15,000 years ago, Bretz’s best guess from the 1920s, made with the only tools he had. In 2017 a team led by Andrea Balbas dated the flood boulders directly, and moved the largest floods back three thousand years.

Getting the number right is part of interpretation too. We carry the corrected science, fully attributed, onto every page.

A four-thousand-year chronology
18.2 kaThe largest floods route down the NW Columbia.
15.6 kaUpper Grand Coulee opens, the later flood path.
14.7 kaThe last major Missoula flood clears the prairie.
14.0 kaThe floods finally stop. The falls go dry.
Peoples of the floods

The water crossed homelands. The peoples of this country carry their own account of it.

The floods reshaped a region that is, and has always been, the homeland of many tribal nations who live here today. A dedicated page shares those accounts in the words of tribal speakers themselves. This is only the doorway to it.

Visit Peoples of the Floods →
Built with
Ice Age Floods Institute National Park Service USGS Terrain360