Huge boulders shown in column at right were deposited by the Ice Age Floods. Top two images show boulders on private property [photos taken from city streets]. Boulders in lower photo sit near Columbia River pedestrian bridge - along bike path.
Ice Age Flood Story
During much of the Pleistocene Epoch, the Okanogan Ice Sheet covered much of north central Washington and blocked the Columbia River north of Wenatchee. As a result, the Wenatchee area did not experience the intense flood erosion experienced elsewhere in Washington. Coulee walls do not tower over Wenatchee. But during times when the ice sheet was smaller in northern Washington, tremendous volumes of water came surging down the Columbia River and the Ice Age flood deposits at Wenatchee were laid down.
Giant flood bars, ice-rafted erratics, fine-grained slack water sediments - these are the features on display in Wenatchee. And the scale of these landforms are truly breathtaking! Pangborn Bar is the king of the region - a giant flood bar 600 feet high. The Ice Age Floods over Wenatchee were 1000 feet deep and traveling quickly down the Columbia!
And it wasn't just floodwater. There were large rafts of ice - broken pieces of the Okanogan Lobe - that floated in on the water carrying large boulders from the north. Ice-rafted erratics of gneiss, granite, and other foreign rocks now litter the local landscape. They are well-traveled boulders that help mark the extent of the floods - not only over Wenatchee, but also plenty of quiet water that worked its way up the Wenatchee River Valley to Cascade town of Leavenworth!