Pegmatite Dikes
Over a billion years ago, molten rock was squeezed into fissures forming the light-colored bands which thread 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 dikes here, combined with their resistance to weathering, has 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 you are standing on! Imagine the relentless cutting power of the Gunnison River.
Erected by National Park Service.
Topics. This historical marker is listed in this topic list: Natural Features
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Location. 38° 33.327′ N, 107° 41.22′ W. Marker is in Black Canyon of the Gunnison National Park, Colorado, in Montrose County. Marker is about 250 feet NNW of the South Rim Visitor Center, on the trail leading to Gunnison Point scenic overlook. Touch for map. Marker is in this post office area: Montrose CO 81401, United States of America. Touch for directions.
Other nearby markers. At least 8 other markers are within 11 miles of this marker, measured as the crow flies. Black Canyon of the Gunnison National Park (approx. 0.3 miles away); Early Exploration (approx. 2.3 miles away); The Painted Wall (approx. 2.4 miles away); Light at the End of the Tunnel (approx. 2.9 miles away); Building a Dam (approx. 2.9 miles away); All Aboard (approx. 10.4 miles away); Narrow Path to Prosperity (approx. 10˝ miles away); Working on the Railroad (approx. 10˝ miles away).
Also see . . . Black Canyon Minerals. (Submitted on October 30, 2020, by William Fischer, Jr. of Scranton, Pennsylvania.)
Credits. This page was last revised on October 30, 2020. It was originally submitted on October 30, 2020, by William Fischer, Jr. of Scranton, Pennsylvania. This page has been viewed 217 times since then and 51 times this year. Photos: 1, 2, 3, 4, 5, 6. submitted on October 30, 2020, by William Fischer, Jr. of Scranton, Pennsylvania.
