Steptoe Butte
Standing more than 1000 feet over the rolling hills that French-Canadian explorers and fur traders called "the grassland" - La Pelouse - is Steptoe Butte. The butte is an island of ancient rock rising above much younger lava flows of Columbia Basin basalt. It is, in fact, such a prototypical example of this type of formation that it has given its name to all other examples - steptoe, which is defined as "an isolated hill, or mountain, of older rock that is surrounded by younger lava flows".
Steptoe Butte began its life as ancient ocean floor. Some 400 million years ago, during the Precambrian era, uplift raised this seabed into an impressive mountain of sedimentary rock. During the Miocene era, layer after layer of lava from the Columbia Basin enveloped it so that today only the summit remains, which is comprised of some of the oldest rock in the state of Washington (see Figure 1). During the retreat of the last ice age, glacial outwash produced huge volumes of wind-blown silt called loess. It blankets much of the Columbia Basin, in places is up to 200 feet thick, and now completely covers the basalt around Steptoe Butte (see Figure 2). It is this loess that forms the rolling hills of the Palouse, and it provides the ideal conditions for growing wheat, making southeast Washington one of the major grain-producing regions of the world.
| Figure 1. A cross section of Steptoe Butte illustrating the older peak of Precambrian rock surrounded by younger lava flows. |
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| Figure 2. Geologic map of the Palouse area of Washington showing steptoes dotting the area as islands among the surrounding deposits. |
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A road spirals its way up Steptoe Butte to the top where one can see in all directions to distant mountains standing beyond endless waves of wheat. The posted coordinates will take you to the benchmark denoting the summit. Immediately adjacent are several interpretive signs explaining the geologic significance and history of Steptoe Butte. To get credit for this EarthCache, please answer the following questions using information available on the interpretive signs and send those answers to me via my profile. Please don't post your answers here, even if encrypted.
- Q1: Of what specific type of rock is Steptoe Butte comprised?
- Q2: How old is the basalt surrounding the butte?
- Q3: How thick is this basalt layer?
- Q4: How large of an area do the rolling Palouse Hills cover?
As you look out from the summit of Steptoe Butte, you might spot a little town 7 miles to the north. That is Oakesdale and is the town in which my father was born and raised. He looked up at this mountain every day for the first eleven years of his life and has many fond memories of it.
The rolling Palouse Hills seen from the summit of Steptoe Butte
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