The Menan Buttes are a prominent feature of the Upper Snake River Valley. What most people don’t know is that they aren’t just random lumps of rock. What makes them unique is that they are cinder cones formed by now extinct volcanoes that erupted up through fresh water. There are similar formations elsewhere in the U.S. that came up in salt water as opposed to fresh. So that hike you take up “R” mountain is really a one of a kind trip.
Words to Know
Cinder Cone—A cinder cone is a type of volcano that forms relatively quickly. It is distinct from other volcanic formations in that it is smaller and the crater at the summit is much larger when compared to the rest of the volcano (crater to volcano ratio).
Xenolith—Means foreign rock. A chunk of rock is incorporated into an igneous rock. The foreign rock may or may not be igneous.
The Menan Buttes can easily be seen from Rexburg (“R” Mountain) and are studied for their uniqueness. The Snake River has been flowing in this area for thousands of years and was one of the most prominent features in this area. The Menan Buttes essentially erupted up through the river bed and formed a cinder cone. The river’s path was greatly interrupted by the sudden appearance of a cinder cone, but over the course of a few years, it developed a new path around the cinder cone.
Because the Menan Buttes erupted through water, the lava cooled too fast to form crystals. There are several places on the Menan Buttes where the rocks cooled so fast, that the bubbles that were in the lava became holes in the rock. It is very rare for a volcano to erupt through a river and as a result, there are many Xenoliths in the Menan Buttes. When the volcano erupted, rocks from the river bed were incorporated into the cooling lava. The way to identify these xenoliths is by looking at the shape and color of them. They will traditionally be rounded (like rocks found in any river) and be lighter in color than the igneous rock that contains them.
North Menan Butte can be explored at leisure through a day-hike trail that circles the upperpart of the cone-like mountain. The hike includes several informative trail signs that allow the hikers to explore not only the Butte, but the panoramic view beneath them of Southeastern Idaho. Make sure you bring plenty of water, as the countryside can be hot and dry at certain times of the year.
Click here to look at the animals you might find on or around Menan Buttes!
For a place to camp overnight nearby Rexburg, take a look at Beaver Dick Park. Not far from the North Menan Butte trailhead or from Rexburg, it provides an excellent place for picnics, water fun, and family camping experiences.