Aspen and Tertiary volcanic rocks and tuff border US Highway 50 approaching Gunnison CO.
The Gunnison River runs through Black Canyon of the Gunnison at Pulpit Rock. The river cut through 1,800 Ma gneiss that was formed from an island arc south of Wyoming Province that would become part of North America. Regional uplift in mid-Tertiary time (30-50 Ma) increased the gradient of the river and strengthened river flow with boulders and gravel and ice from Pleistocene Age glacial melt off to accelerated canyon cutting.
Black Canyon of the Gunnison at Cross Fissures View.
2300 foot Painted Wall, Black Canyon of the Gunnison. 1800 Ma gneiss was penetrated by veins of pegmatite powered by a 1,400 Ma intrusion of granite pushing hot fluids rich in feldspar and quartz that crystallized as it cooled to form pegmatite.
Panorama of Painted Wall, Black Canyon of the Gunnison
Stop at Monarch Pass on US Highway 50 on way to Gunnison
Tomichi Dome, a Tertiary laccolith, formed when magma was forced out through and above Cretaceous Dakota sandstone and into Mancos shale to form a dome. Sandstone and shale were subsequently eroded away. West of Sargents CO on US Highway 50.
Partially-eroded pinnacles of West Elk breccia from mid-phase Tertiary volcanics rest on Mesozoic sediment above Blue Mesa Reservoir.
Terraced layers of rhyolitic brecca and tuff above Mesozoic sediment by Blue Mesa Reservoir.
Weathered gneiss with pegmatite veins and lichen, Black Canyon of the Gunnison
Three geologic formations: Bottom – Black Canyon of the Gunnison gneiss and pegmatite (1.8 to 1.4 billion years); Middle: Mesozoic eroded sediment (60-90 Ma); Top – Igneous laccoliths of Landsend Peak (left) and Mount Lamborn (right) (~11,000’), West Elk Mountains (23-33 Ma) intruded into sediment and then eroded to igneous rock.
Closeup of pegmatite vein dominated by pink K-feldspar.
