3. The Crown Butte Story

Approaching the Cliffs on the East Side of Crown Butte

Three hikers are headed toward the eastern edge of the Crown Butte where the plaque (shown below) can be found. Crown Butte is located between Great Falls and the Rocky Mountains, along the southern end of what Montanans refer to as "the Rocky Mountain Front". The butte was purchased by the Nature Conservancy in order to preserve the natural grassland ecosystem located on top of the butte. Except for an occasional hiker, the ecosystem sits undisturbed about 1,000 feet above the surrounding northern great plains.

The butte's geologic past . . .
Crown Butte is one of four buttes located in the area west of Great Falls. All four are "laccoliths" that were formed during a period of volcanic activity from 71 to 81 million years ago*. Some of the magma worked its way laterally through vertical fractures in surrounding sedimentary rock layers. In places, the magma's upward movement was halted by a durable layer of sandstone which domed upward as the magma pooled below. Eventually the magma hardened, creating a network of dikes and laccoliths beneath the surface. Erosion has worn away hundreds of feet of overlying sedimentary rock, leaving remnants of the more resistant igneous formations.

Square Butte, which can easily be seen from the highway between Great Falls and Cascade (see photo below), is the most prominent of the four buttes. Dikes from the buttes form ridges that stand over 50 feet high that can also be seen converging near the town of Cascade, 20 miles southeast of Crown Butte. The dikes provided pathways for molten rock to move from the magma chamber to the laccoliths ("lakes of rock") . . . All of this happened under ground (intrusive). Proceed to the next page to learn more.

*Source: Sheriff, S.D., and Gunderson, J.A., 1990, "Age of the Adel Mountain volcanic field, west-central Montana": Isochron/West, no. 56, p 21-23.