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<\/body><\/html>') newWindow.resizeBy(picWidth-newWindow.document.body.clientWidth,picHeight-newWindow.document.body.clientHeight) newWindow.focus() } //--> Home Page Not much time? ... Click here for a quick Ice Age Floods summary Ice Age Floods Feature of the month For many years one man understood the clues but no one would listen Glacial Lake Missoula Channeled Scablands of Eastern Washington Temporary Lake Lewis Columbia Gorge Explore the variety of features created by the Ice Age Floods Columbia River Basalt Group The Pleistocene Grand Coulee Dam and the Columbia Basin Irrigation Project Washington Wines Ice Age Floods Institute
Bax Barton, Burke Museum.

Bax R, Barton describes mammoth bones found at the Coyote Canyon Mammoth Dig [Kennewick, WA].

Pleistocen Mammoth.


Yeager Rock Ice Age.

Yeager Rock [Mansfield, WA.] was left stranded at this location when the Okanogan Lobe of the Cordilleran Ice sheet retreated. See Yeager Rock viewed from north at bottom of this page.

The flood torrents that gushed from Lake Missoula were possible only because the region was in the grip of the Ice Age. But Lake Missoula’s weren’t the only floods, and other outflows thousands of years earlier may have been even more spectacular.

Between 2 million and 2.5 million years ago the Earth’s climate changed. Glacial ice sheets advanced southward, and then retreated. These cycles repeated several times. Certain individual glacial periods may have lasted for several thousand years, followed by lengthy dry and warmer periods.

Click above to play short documentary on Wenas Creek mammoth excavation near Central Washington University.

The Ice Age had profound impacts upon the Pacific Northwest and the Columbia Basin. At their greatest extent, glaciers and ice sheets covered all of the Puget Sound lowlands, coated all but the higher elevations of the North Cascades and other mountain ranges north of the Columbia River and Lake Roosevelt, and dominated the landscape of the Idaho panhandle and northern Montana.

Elsewhere in North America, the advancing ice sheets blanketed the northern plains and extended southward to the Ohio River. In the process, the glaciers gave the Great Lakes their modern shape - and created some of the most valuable farm land to be found anywhere in the world.

Glacial Debris - North Central Washington

Huge granite boulders moved by glaicial ice during the Pleistocene.
The receding Okanogon Lobe left many huge granite boulders stranded on the basalt.

Huge basalt left behind by the receding ice lobe at the end of the most recent ice age.
The Ice Age left challenging obstacles and terrain for area wheat growers.

Farming around glacial debris.

Basalt erratics near Pateros, WA.
Basalt Erratics

Columbia Basin erratics are found scattered over basalt bedrock. North of Wenatchee (beyond the reach of Columbia River Basalt flows) many of the erratics are basalt that were moved to present day locations within ice.

Balanced Rock near Omak Lake.
Interesting balanced rock near Omak Lake

View Larger Map
Use Google's map navigation tools to explore glacially
influenced terrain SW of Omak Lake.
Ice Age basalt boulders left by the Okanogan Lobe of the Cordilleran Ice Sheet.
Home for scale


When dealing with water, scientists speak of the “hydrologic cycle.” A primitive description can be found in the biblical Book of Ecclesiastes: “All the rivers run into the sea; yet the sea is not full; unto the place from whence the rivers come thither they return again.” If only it were that simple. Water exists as liquid, solid, or vapor. There is a finite total amount. Water is either impounded in oceans, lakes and ponds…moving in rivers or underground aquifers…temporarily invisible as vapor until it returns to the surface as precipitation…or is trapped as ice.

During the later stages of the Ice Age so much water had been transformed into glacial ice that the world’s oceans were 300 feet lower than they are today. The impact may have been more dramatic at an earlier stage of the Pleistocene Epoch, because evidence suggests that at one time the oceans were 450 feet below modern levels.

For the hydrologic cycle to be so dramatically altered by glacial activity, only two factors matter. The climate must be wet enough to generate considerable precipitation. The climate also must be cool enough that winter snowfall exceeds summer snowmelt. Lingering snowfall eventually compacts into glacial ice. Cold weather by itself won’t create an ice age.

Therefore, at the onset of the Pleistocene Ice Age the Earth’s climate changed enough so that the interplay of temperature and precipitation triggered the expansion of glacial activity. Fluctuations in these conditions caused the periodic advances and withdrawals of the ice masses. There is no fully-accepted view of what caused the climate change. Some scientists believe that the Earth’s orbit around the Sun undergoes periodic minor fluctuations that are sufficient to create climate conditions like these.

For many years students were taught that there were four major glacial outbreaks. It is now believed that there were at least eight, and perhaps as many as 20. Since the later glacial extensions would have eradicated most evidence of the earlier ones, precise knowledge may always elude researchers.

Geology of Seattle and the Puget Sound video

Recent glacial events in the Puget Sound region are described in this video. Amazing that the Seattle area was under 3,000 feet of ice!


The Ice Age floods—at least the ones we know about—were products of the Wisconsin glaciation, which began about 100,000 years ago and ended about 10,000 years ago. In addition to the Lake Missoula floods of 15,000-20,000 years ago, it is believed that even more cataclysmic floods took place between 50,000-60,000 years ago.

Less is known about Glacial Lake Columbia, which roughly amounted to a greatly-expanded version of modern day Lake Roosevelt—which consists of the water impounded behind Grand Coulee Dam. It is believed that during the Wisconsin glacial era Lake Columbia’s surface was about 1,000 feet higher than today’s surface elevation of Lake Roosevelt. Geologists also think that Lake Columbia was not subjected to periodic catastrophic floods caused by ice dam failures.

Skagit Valley fields once covered by the the Puget Lobe during the Pleistocene Ice Age.
The Skagit Valley - Today famous for bulb production, was buried under the nearly one-mile thick Puget Lobe of the Cordilleran Ice Sheet.

Lake Columbia was formed as a result of blockage created by a lobe of an ice sheet that spread down the Okanogan Valley, crossed the Columbia River, and then spread over 500 square miles of the Waterville Plateau. Advancing glaciers push huge accumulations of rocks and soil in front of them. When glaciers later retreat these mounds, some of them hundreds of feet high, remain as evidence in the form of “terminal moraines.” Withrow Moraine, west of Dry Falls and north of U.S. Highway 2, marks the southernmost reach of the Okanogan glacial lobe.

It seems clear that Grand Coulee and Moses Coulee were not formed entirely by the Lake Missoula floods, but initially were scoured by meltwater and runoff from Lake Columbia at an earlier time. Overflow water from Lake Columbia occupied Grand Coulee between flood events. However, substantial flood episodes were involved in the phenomenal natural feature of Dry Falls, near Coulee City. Dry Falls is a three-mile-wide complex of cataracts that during the Ice Age dropped water 400 feet. The force of floods and runoff was sufficient to dislodge basalt columns forming the lip of the falls. Over time the falls “retreated” 15 miles northward through Grand Coulee.

Another glacial lobe in northeastern Washington created Lake Spokane, which at times may have been an extension of Lake Columbia. The glacial lobe which filled the Purcell Trench in the Idaho panhandle—and provided Lake Missoula’s ice dams—was 20 miles wide. Nearly all of the higher mountains in northwest Montana had large glaciers on their slopes during the Ice Age, and the glaciation was so extensive that it almost represented a continuous ice sheet. An extension of the Rocky Mountain Trench of British Columbia contained an immense valley glacier that was 6,000 feet deep at the U.S.-Canada border. Other glacial lakes may have been formed as the result of ice dams especially in the channel of the Kootenai River.

West of the Cascade Range, meanwhile, thick glacial ice sheets penetrated southward into the broad valleys of the Puget Sound lowlands--which at that time were dry land, except for several rivers. The southernly limit of the ice mass was reached a few miles beyond today's Olympia. Ice Age meltwater and runoff drained westward to the Pacific Ocean via the Chehalis River gap.

Glaciers filled and leveled the region, gouging out channels and trenches that later would become such terrain features as Puget Sound, Lake Washington and Hood Canal. Ice-borne "erratic" rocks from British Columbia have been found in the low country east of Puget Sound and on the islands within the sound and Admiralty Inlet. A number of hills and lesser mountains west of the main stem of the Cascades had their tops rounded by the advancing ice, which was 2,500 feet deep as far south as Seattle. Huge chunks of ice separated from the ice masses and were buried among the sediment deposited during the Pleistocene Epoch. As this buried ice eventually melted--a process that extended over many years--the result was a number of depressions in the landscape known as "Kettles."

Wedgewood Erratic, Glacial Erratic Boulder Seattle, WA. - Teresa Foster

Teresa Foster inspects glacial erratic boulder [Wedgewood Erratic] north of University of Washington campus.

The Wedgewood Erratic was placed at this location [NE 72nd Street and 28th Avenue NE] by the Vashon Glacier. Other large Puget Sound area erratics are described in blog posts by Dave Tucker.


The Ice Age encompassed two million years of amazing events which helped shape the geography and geology of the Columbia Basin. What surprises scientists the most is how abruptly it ended. Within a geologically brief time span of about 5,000 years the glaciers retreated to approximately their present ranges. Ocean levels had been raised to their modern shorelines by 10,000 years ago—when the Ice Age ended.

Huge basalt boulders scattered over the Waterville Plateau.
Use Google Maps or Google Earth to view Waterville Plateau "Haystack Rocks" from above.

Farmers forced to remove or pile countless boulders and stones left by the retreating icesheet.
Piles of Ice Age dropstones and erratics are often found on field margins in the Mission Valley, Columbia Basin, Yakima Valley, Umatilla Basin and Willamette Valley. On the Waterville Plateau, many fields contain multiple piles of boulders and stones left by the ice lobe.

Freeze-thaw cycles slowly breakdown haystack rocks.
Freeze-thaw weathering adds shattered basalt to pile at base of haystack rocks.

The clam haystack rock.
Crack them open and you'll find more basalt.

Waterville Plateau maps and directions.
Detailed maps help when exploring the Waterville Plateau and Timentwa Flat.

Click to open USGS: Ice Sheets and Glaciations Page

For current status of glacial ice in the North Cascades visit:


Yeager Rock and other haystack rocks stranded on Mansfield Plateau near Mansfield, WA.

Yeager Rock [center] sits among similar haystack rocks that were carried to this location by Okanogan Lobe of the Cordilleran Icesheet.

All photos by Tom Foster unless otherwise noted.

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