Crown Butte, Montana

December 18, 2017


Crownbutte_viewPhotographer: Rod Benson
Summary Author: Rod Benson 

The photo above shows some nice columnar jointing on Crown Butte, a laccolith situated at the southern end of the Rocky Mountain Front, some 30 miles (48 km) west of Great Falls, Montana. Crown Butte and vicinity is one of my favorite places to take hikers, especially students, from the Helena High Outdoors Club. It's reasonably close to Helena, there's public access and the 5-6 mile (8-10 km) round trip hike can be done in an afternoon. Note that the elevation gain is approximately 900 ft (274 m). Crown Butte offers amazing vistas of distant mountains in all directions (photo at left). The geology here is interesting as well.

The Crown Butte laccoliths formed during a period of volcanic activity, roughly 70-80 million years ago. The actual volcano was located between current day Craig and Cascade – you drive by it on I-15 between Great Falls and Helena. When the volcano was active some of the magma beneath it worked its way laterally through vertical fractures in surrounding rock layers. In places, the magma’s upward movement was halted by a durable layer of sandstone that domed upward as the magma pooled below. Eventually the magma hardened, becoming rock. Then in the millions of years that followed, erosion removed hundreds of feet of overlying sedimentary rock, exposing remnants of the more resistant igneous formations (the buttes).

Photo Details: Top - Camera Make Panasonic; Model DMC-LX7; Exposure Time 0.0008s (1/1300); Aperture ƒ/2.8; ISO equivalent 80; Focal Length (35mm) 47;  Software QuickTime 7.6.6. Inset - same except: Exposure Time 0.0006s (1/1600); Focal Length (35mm) 65.