Photographer: Ray Boren
Summary Author: Ray Boren
As if slices had been cut into a marbled cake of titanic size, curiously striped dark cliffs near Montrose, Colorado, rise precipitously above a roaring river, far below — a testament to geologic events well over billion years ago (and since) at what is today treasured as Black Canyon of the Gunnison National Park.
The grandeur is evident along scenic drives on Black Canyon’s rims, as illustrated in the photo above, taken at the South Rim’s Painted Wall overlook on May 21, 2017. At 2,250 ft (686 m) in height, the wall is considered to be the tallest cliff in Colorado. The Gunnison River, visible on the left, was named for 19th-century military officer and topographical surveyor Capt. John W. Gunnison. A second photo, taken at the Cross Fissures pullout, also shows snowy summits of the Sawatch Mountain Range, the source of the Gunnison.
For millions of years the river has been eroding a remarkably deep and narrow gorge through Precambrian rocks of the Gunnison Uplift. The uplift dome is composed mostly of dark metamorphic gneisses and schist, banded with pinkish pegmatite dikes, flecked with crystalline minerals like quartz, mica and feldspar, and even garnet. The sheer cliffs’ pegmatite veins were originally molten rock, or magma, which squeezed, or intruded, into fissures within the already-hardened gneisses and schist deep within the Earth. In some places the pegmatite, a granite more resistant to erosion than the surrounding rock, shows up in vertical fins; in others it manifests as serpentine bands that pattern the darker rock, as on the Painted Wall.
Like a long white-water waterfall, the Gunnison drops farther in 48 mi (77 km), as it cuts a trench through its sun-deprived and therefore black canyon, than the mighty Mississippi does in its 1,500 mi (2,414 km) journey from Minnesota to the Gulf of Mexico, the Park Service notes. Rim to river, the canyon walls range in height from 1,750 ft to 2,772 ft (533 to 845 m). Black Canyon was set aside as a national monument in 1933. In 1999 Congress passed, and President Bill Clinton signed legislation that expanded the boundaries and created Black Canyon of the Gunnison National Park.
Photo Details - Top: Camera Model: NIKON D3200; Lens: Tokina AT-X 124 AF PRO DX II (AF 12-24mm f/4); Focal Length: 12mm (35mm equivalent: 18mm); Aperture: ƒ/11.0; Exposure Time: 0.017 s (1/60); ISO equiv: 100. Bottom - same except: Lens: AF-S VR Zoom-Nikkor 70-300mm f/4.5-5.6G IF-ED; Focal Length: 70mm (35mm equivalent: 105mm); Exposure Time: 0.0020 s (1/500); ISO equiv: 400.