Natural Features & Ecosystems

Geology and Ice Age Floods

 
Aerial view of sloping cliffside of brown rocks emerging out of bright blue water.
Geology

Granite, basalt, and large coulees make the complex puzzle that is Lake Roosevelt.

Wide gorge of brown and orange rock with a reflective blue lake and small plants growing around it.
Ice Age Floods National Geologic Trail

At the end of the last Ice Age, great floods crashed through the landscape, sculpting the northwestern United States.

 

Lake Roosevelt National Recreation Area spans three distinct geologic provinces: the Okanogan Highlands, the Kootenay Arc, and the Columbia Plateau. The landscape has been shaped by gradual forces of uplift and erosion, and by sudden cataclysmic events. Over millions of years, intermittent lava flows created the Columbia Basin. Tectonic action later uplifted these volcanic basalt layers. The Cascade Mountains rose and created a rain shadow, reducing the amount of precipitation in the Columbia Basin and Okanogan highlands. During the last Ice Age, a series of massive floods scoured the coulees and created the channels scablands.

 

Ecosystems

 
Narrow tan grasses stick out on a dry landscape with shrubs overlooking a vast lake.
Channeled Scablands

This shrub-steppe ecosystem is filled with large shrubs, broadleaf wildflowers, and a large diversity of grass species.

Tall pine trees line a wide dirt pathway.
Okanogan Highlands

An extension of the Rocky Mountains, this ecosystem has a more mountainous climate and is dense with conifers.

 

Lake Roosevelt marks a transition zone between the desert-like Columbia Basin to the south and the slightly wetter Okanogan Highland to the north.

Fish inhabiting Lake Roosevelt continue to adapt to an altered environment: dams have stopped salmon and sturgeon runs, the lake's depth fluctuates seasonally because of snowmelt runoff, the water temperature varies at different locations, and human-introduced species like kokanee and walleye compete with native fish populations for food and habitat.

Much of the shoreline around Lake Roosevelt supports conifer forests, grasslands, and scrublands that provide habitat for an estimated 75 species of mammals, 200 species of birds, 15 species of reptiles and 10 species of amphibians.

The area's plant and animal species have changed and continue to change overtime, adapting to climate transitions that vary from location to location.

Last updated: August 20, 2023

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Contact Info

Mailing Address:

Lake Roosevelt National Recreation Area
1008 Crest Drive

Coulee Dam, WA 99116

Phone:

509-754-7800
Please leave a detailed message if no one answers your call. Our rangers are often out talking to visitors.

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