Snake Butte Laccolith
November 03, 2020
Photographer: Rod Benson
Summary Authors: Rod Benson
Snake Butte is a 2.6 mile (4.1 km) long laccolith located on the Fort Belknap Reservation in north-central Montana. The magma that became the butte originated from a volcanic center, which formed the Bears Paw Mountains several miles to the southwest. The Bears Paw Mountains, shown in the background, are remnants of volcanoes that were active some 50 million years ago. In the millions of years since the laccolith hardened, the less durable sedimentary rock above and around it eroded away, exposing the igneous rock of Snake Butte. The fence-like appearance of the cliffs shown in this aerial photo is due to columnar jointing, which occurred as the magma cooled.
During the 1930s, the durable rock of Snake Butte was used to build the causeway at the Fort Peck Dam on the Missouri River in northeastern Montana. The quarry area can be seen along the right side of the butte in the photo. Snake Butte is interesting for several other reasons, including its significance as a sacred place for the tribes of the Fort Belknap Reservation, and the clues left there by the Laurentide Ice Sheet thousands of years ago. Photo taken August 17, 2020.