The Mountain That Is Not a Butte
Near Crested Butte, Colorado
Look up at the peak that towers over town, the one shaped like a crooked crown. It rises to about twelve thousand one hundred sixty feet, and despite its name, it is not truly a butte. Geologists call it a laccolith.
About thirty million years ago, molten rock pushed upward from deep underground and forced its way into a layer of soft gray shale called Mancos Shale. Instead of erupting at the surface, the magma spread out and hardened into a dome of tough igneous stone, quartz monzonite and granodiorite porphyry. Over the ages that followed, the softer shale around it eroded away, and the hard core was left standing alone, a mountain built from the inside out.
Crested Butte is only one of more than a dozen such laccoliths scattered across the Elk Mountains and the neighboring West Elk range. When that hot magma pushed into the surrounding rock, it also cooked and altered it, and it seeded the ground with minerals. Those same intrusions are the reason miners came here in the first place, chasing silver, then coal, and much later, a vast deposit of molybdenum hidden inside a nearby peak the town would fight for decades to protect.
