Uncompahgre Uplift Basement
The ~1.7-billion-year-old Paleoproterozoic gneiss, schist, and granite of the Uncompahgre uplift — the black inner gorge of Westwater and the Black Rocks of Ruby Canyon.
Also known as: Westwater basement, Black Rocks basement, Black Quartzite / Metamorphic Suite
Proterozoic — long before animals, a world of microbes and bare rock
The world back then
1.7 billion years ago there is no river, no canyon, no you. This rock is kilometers down in the crust — gneiss and granite forged in the roots of a mountain range as continents collided to build North America. Crushing heat and pressure, total dark, and above it a bare, lifeless world with nothing alive but single-celled scum in a shallow sea.
Skip past the entire history of life and here's your reward: a boat, a cold drink, and a wall of the planet's oldest bones sliding by while you do nothing but watch. Complaining is the human birthright — but drifting past deep time in the shade, un-hunted and unhurried, is about as good as it has ever gotten for anybody.
Recognize it in the field
- Typical color
- dark gray to black (gneiss, schist, amphibolite); pink to gray granite and pegmatite
- Weathers as
- Hard, non-erodible crystalline rock — the dark, polished inner-gorge walls of Westwater Canyon and the Black Rocks of Ruby Canyon, constricting the river into steep bedrock rapids.
- Grain
- coarse, crystalline
Look for
- dark gneiss, schist, and amphibolite intruded by granite and pegmatite
- the ~1.7-billion-year-old basement of the Uncompahgre uplift, the oldest rock on the run
- forms the black inner gorge of Westwater and the Black Rocks of Ruby Canyon
- overlain by Triassic beds across the Great Unconformity (~1.5-billion-year gap)
- correlative in age with the Grand Canyon's Vishnu Schist / Zoroaster Granite, but a distinct, informally unnamed body
How this rock was made
Deep-crustal Paleoproterozoic metamorphism (~1.7 Ga) and plutonism, exposed today in erosional windows through the Uncompahgre uplift.
The setting: metamorphic and igneous basement (not deposited) — amphibolite-rock types (facies) gneiss and schist intruded by granitoids
A basement complex, not a bedded unit — exposed in erosional windows in the Uncompahgre uplift of Colorado and Utah (Case, I-2088).
In the rock record
↑ Younger — rests above
Where to see it
Regions: Uncompahgre uplift (Colorado Plateau)
- Westwater Canyon inner gorge (Colorado River)
- Black Rocks, Ruby Canyon (Colorado River, Black Ridge Canyons)
Float past it: Westwater Canyon · Ruby–Horsethief Canyon