Overview and
Geological History

Buckle up and blast off to Mars on this virtual tour of eastern Washington. We'll begin with an overview of the area and some of the geological history. The trip examines over thirty points of interest and images from Mars are included for comparison. For convenience each page has a list of related geology terms or use the Define Word button at left.

Overview

Basalt rock up to 10,000 feet thick and consisting of more than 300 lava flows run for miles and miles under the semi-arid skies of eastern Washington. Some flows are over 90 feet deep. Beneath these massive layers is bedrock from earlier volcanic activity. On top of the granite bedrock we find sediment layers from glacial lakes, boulders and debris from glaciers, channels in the basalt and gravel bars left by giant floods, and fertile loess (fine dirt) blown in on the winds.

The map at right by Ray Sterner, Johns Hopkins University shows the mountains and rivers (dark blue) of the area. The different colors indicate elevation and the red lines show state boundaries. Click here for a larger (75K) image or a full size (196K) image. You can see the channels and flat area of the plateau (orange, yellow and green). Spokane, near the eastern edge of Washington, is where we begin. The Spokane River flows through the city and on to Franklin D. Roosevelt Lake, a part of the Columbia River behind Grand Coulee Dam. For the text that accompanies the image click on Digital Relief Map Text.

We will take highway US 2 heading west, travel southwest on state highway 28 and others to discover Banks Lake, Grand Coulee Dam, and Dry Falls. A spot near Ephrata is similar to the Ares Vallis area where the Mars Pathfinder mission landed. While we are on our way back to Spokane on Interstate 90 we'll learn more about the giant floods and discuss volcanoes and the Mt St. Helens eruption of 1980, earthquakes, sand dunes, dust devils, and other features found on Mars and Earth.

As a review here are some facts about the two planets. Mars (6794.4 km in diameter) is about half the size of Earth (12,756.28 km in diameter). Mars has a temperature range of -140° C to 20° C while Earth has a range of -69° C to 58° C. Mars rotates in 1 day, 0.67 hours and takes about 2 years to complete one orbit around the sun.

Geological History

Some 200 million years ago the western edge of the North American continent was about 60 miles west of where Spokane is now. Fossils of ocean plants and animals have been found in the now-dry eastern Washington area. How did this lush seacoast become a semi-arid desert? The story continues on the Geological History page or skip to NEXT page.

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Geology Terms

Here are some basic terms used in the tour. Find more geology terms in the Glossary.

Basalt

Volcanic rock caused by partial melting of the Earth's crust.

Bedrock

Solid layers of rock in the Earth's crust beneath soil.

Coulee

Long winding channel cut through lava formations.

Geomorphology

The study of the changes in landforms due to volcanoes,
earthquakes, weather, floods, etc.

Gneiss

Metamorphic rock with bands or or streaks.

Granite

Coarse-grained igneous rock usually without obvious bands or markings.

Loess

Fine dirt deposited by wind usually from arid or glaciated areas.

Volcano

A vent at the surface where magma, gas and steam erupt. Also, the landform constructed by volcanic material.

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