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Pegmatite Dikes:
Over a billion years ago, molten rock was squeezed into fissures forming the light-colored bands which threat Black Canyon's otherwise dark walls. You are standing on one of these bands. As the hot fluid slowly cooled and hardened, minerals formed into crystals. Look closely; you may recognize flecks of mica, feldspar, quartz, and perhaps even garnet.
These bands of lighter colored igneous rock -- called pegmatite dikes -- are more resistant to erosion than the dark gneisses (sounds like "nice-es") into which they intrude.
Consequently, the pegmatite weathers more slowly than the gneiss. The vertical position of the hikes here, combined with their resistance to weathering, had produced the fin-like appearance of parts of the canyon walls. You will see pegmatite at nearly every overlook.
The pegmatite dike you see across the canyon nearly half a mile away is the same one your are standing on! Imagine the relentless cutting power of the Gunnison River. |