Grand Coulee Dam to Dry Falls 2

Crown Point Vista, Haystack Rocks and Lakebeds
Continued

[175.6 MM 1]
We are at the junction of Highway 174 with State Highway 17 South where we turn left.

[176.8 MM 120]
For the next few miles we see old lakebeds, glacial tills and glacial outwash in the road cuts.

As the ice age glaciers melted and retreated they left behind the sand, gravel and rocks they were carrying. The material is piled into mounds called a till. Deposits of rocks, boulders, gravel and sand (called glacial drift) left behind by flowing water from glaciers as they melted is called glacial outwash.

In the photo at right you can see that the glacial tills have left behind a variety of rocks, gravel and sand. At the top are smaller cobbles(larger rocks) with midsized rocks in the middle. At the bottom is dark basalt gravel and rocks. Mixed in with everything is sand and gravel.

[183.8 MM 113]
The lakebed photo below is in a road cut on the left. Click here for a detail image or close detail image of the lakebed. There is a golfball placed in the detail images to give you an idea of how thin the layers of fine sand and silt are.

Lakebed in road cut. Click for detail image or close detail image.

[184.5 MM 112]
To the right in the distance is an esker, a sinuous ridge formed by glacial action. These narrow, winding ridges are made of gravel and are usually formed by streams flowing on a glacier or in a tunnel below the glacier or ice sheet. In the image at right you can see these narrow, winding ridges on the floor of Argyre Basin on Mars. This indicates that at some time glaciers moved over this area on Mars and running water left these formations. See more about glaciers on Page 16 - Glacial Lake Missoula.

[192.4 MM 104]
This erratic rock sits on top of a glacial till in the road cut. It is about the size of a school bus. The basalt rock has partially settled into the sand, gravel and cobbles (larger rocks) that are up to the size of a dinner plate.

[197.4 MM 99]
Here we are at the junction of Highway 17 with Highway US 2. As we turn left (east) onto US 2 we can see Banks Lake and the Dry Falls area up ahead. Continue to next road junction [199.1] and turn right onto State Highway 17 South again. Banks Lake will be behind us and the Dry Falls Museum and Overlook will be just ahead. The view below is from Banks Lake Dam. The earthen dam was built to hold water for irrigation. The water is pumped in from Lake Roosevelt behind Grand Coulee Dam.

Banks Lake fills most of the Lower Grand Coulee.
You can see the nearly vertical walls of the Lower Grand Coulee
that we saw on our way up to Grand Coulee Dam.

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.

Erratic

Large rock or boulder carried by water or glaciers and left behind.

Esker

A narrow, winding ridge made of gravel usually formed by streams flowing on a glacier or in a tunnel below the glacier or ice sheet.

Moraine

Deposits of rocks, boulders, gravel and sand (called glacial drift) left behind by glaciers as they melted. Terminal moraines are at the end of a glacier.

Outwash

Deposits of rocks, boulders, gravel and sand (called glacial drift) left behind by flowing water from glaciers as they melted.

Outwash Plain

A smooth plain covered by deposits from water flowing from glaciers.

Sediment

Collection of sand, silt, gravel and organic material that sinks to the bottom of a river, lake or ocean. Some or all of these materials may be present.

Sedimentary Rock

Rock formed by pressure and accumulation, e.g., lakebeds changed into rock form loose sand, silt and organic materials.

Till

Deposit from a glacier of unsorted rocks, boulders, gravel and sand (glacial drift).

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