Grand Coulee Dam
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Grand Coulee Dam and Roosevelt Lake
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[145.2 MM 25]
Just before we enter Grand Coulee we could take an optional short (3 mile) side trip on State Highway 174 East to look at some pillow basalt. The road takes us up the canyon with a view of Roosevelt Lake and the basalt as shown at right. The pillows range in size from that of a baseball to a football. Click image or here for a larger view. Return to 155 North to continue the trip.
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"The characteristic "pillow" texture exhibited in this road cut is typically manifested when molten lava enters water on land (such as a lake or stream channel), or erupts in a submarine environment. Instant quenching creates the bulbous forms of fractured basalt surrounded by the yellow glassy matrix (consisting of the mineral palagonite and sometimes opal)." [Buchanan] |
[145.2 MM 25]
Passing through the town Grand Coulee we see Franklin D. Roosevelt Lake, named after the 32nd President. In this view from a scenic roadside stop we are looking uplake to the northeast. The lake extends 151 miles with 600 miles of shoreline. Looking to our left is the top of Grand Coulee Dam. The huge sand pile in the background (center) is left over from construction and although used to sand the icy roads in the winter still dwarfs the town of Coulee Dam. See a close-up picture on the Grand Coulee Dam page by clicking below.
Top of Grand Coulee Dam (left) and looking up Roosevelt Lake (right).
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There is a Visitor Arrival Center (VAC) hosted by the US Bureau of Reclamation (photo at right) just below the dam. After the sun goes down, May through September, a narrated laser light show plays across the water spilling down the front of the dam telling the story of the project. The light is beamed up to 4,000 feet from the VAC and creates an image 300 feet high.
Continuing down the hill in front of the dam we cross a bridge to Coulee Dam. On the sidewalks of the bridge look for an informative interpretive walk of the building of Grand Coulee Dam.
If you have time you may take a tour of the dam. The tour takes you on a glass-front inclined elevator that travels 465 feet. You can also take a tour of the Third Powerplant to see the hydro-electric generation units. Information is available at the Visitor Arrival Center.
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More About Grand Coulee Dam
An incredible feat of ingenuity and hard labor, Grand Coulee Dam is a modern wonder. The US Bureau of Reclamation began to construct Grand Coulee Dam in 1933 during the Great Depression. The project took nine years to build and is one of the largest concrete structures in the world. Click here to learn more about Grand Coulee Dam or go on to the next page.
Geology Terms
Here are some basic terms used on this page. Find more geology terms in the Glossary.
- Basalt
- Volcanic rock caused by partial melting of the Earth's crust.
- Channeled Scabland
- Area in Washington state where huge floods made channels in a large, deep basalt flow. Named by J Harlan Bretz during the 1920's in various publications. See also Channeled Scabland and Glacial Lake Missoula.
- Coulee
- Long winding channel cut through lava formations. A term primarily used in the northwestern United States.
- Erratic
- Large rock or boulder carried by water or glaciers and left behind.
- Granite
- Coarse-grained igneous rock usually without obvious bands or markings.
- Gravel
- Rounded rock fragments larger than sand.
- Ice Age
- A period in Earth's history when much of the continents are covered with ice sheets and glaciers.
- Palagonite
- Pale yellow, glassy material that forms when hot steam and other gases contact water during a lava flow. Sand and clay is usually mixed in as well.
- Pillow Basalt
- Basalt formed underwater or as a basalt flow contacts a river or lake.
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