Group · quartzite

Uinta Mountain Group

The four-to-seven-mile-thick Neoproterozoic red quartzite at the core of the Uinta uplift — the walls of the Gates of Lodore, ~770-740 Ma.

Also known as: Uinta Mtn Group

Proterozoic — long before animals, a world of microbes and bare rock

The world back then

Neoproterozoic, roughly 750 million years ago. A deep fault-bounded basin is filling with miles of sand and mud as the supercontinent Rodinia tears apart — an ocean of sediment piling into a rift, layer on layer, with no animals anywhere on Earth to witness it. Just water, sand, and the slow violence of a continent splitting. Utterly empty and utterly enormous.

That four-to-seven-mile pile is the red quartzite core of the Uintas and the walls of the Gates of Lodore, and you float straight into it in the light. It's older than animals; it waited three-quarters of a billion years for eyes to show up. Yours are the ones that made it. Try to look up.

Trail Talk

The non-geologist version — for when someone starts nerding out and you want in.

The gist: The deep-red quartzite core of the Uintas — miles of ancient hardened sand that make the walls of the Gates of Lodore.
Drop this: It's four to seven miles thick and about 750 million years old, laid down before animals existed. Lodore's rapids are where it refuses to erode.
Or just say: Older than animals. The river just has to deal with it.
Rock band: Deep red and purple and white quartzite, miles of it, standing in the sheer walls of the Gates of Lodore — the ancient heavy foundation of the whole range. Old, dense, and glowing red at the right hour. The oldest, heaviest riff on the river, man. It's been holding the low end for 750 million years.

Recognize it in the field

Typical color: red to white and purple
Weathers as: Massive cliff-forming red quartzite — the high peaks of the Uintas and the sheer walls of the Gates of Lodore.
Grain: coarse

Look for

four-to-seven-mile-thick Neoproterozoic quartzite
red-and-white/purple quartzite and conglomerate
the most widely exposed unit in the range (~140 mi of outcrop)
deposited in a rifting Rodinia basin, later inverted into the Uinta arch

How this rock was made

A fault-bounded Neoproterozoic basin on a reactivated suture in SW Laurentia during the breakup of Rodinia; later inverted into the initial Uinta arch.

The setting: marine and river (fluvial) (an intracratonic rift basin)

~13,000-24,000 ft (4.0-7.3 km) where fully preserved.

In the rock record

↑ Younger — rests above

Lodore Formationa huge gap — the Great Unconformity (nonconformity) · Uinta uplift

Browns Park Formationa tilted gap (angular unconformity) · eastern Uinta flank / Browns Park

Uinta Mountain Group you are here

See the full regional rock columns →

Where to see it

Regions: Uinta Mountains (Middle Rocky Mountains province; NPS files Dinosaur NM under Colorado Plateaus)

the core of the Uinta Mountains and its high peaks
Gates of Lodore / Canyon of Lodore (Green River, Dinosaur NM)

Float past it: Lodore Canyon · Whirlpool Canyon · A Section · B Section

Below Flaming Gorge Dam, the A (Spillway to Little Hole) and B (Little Hole to Indian Crossing) sections cut Red Canyon straight into this quartzite — catch a fish while you stare back at 750 million years of history.