GEOLOGY HAPPENINGS - July 2024

Back when I was a park ranger in Canyonlands National Park and interacted with folks at Grand View Point, it was not uncommon for someone to say to me, “This is better than Grand Canyon.” Because of its iconic status and immense size, Grand Canyon serves as a frame of reference for many things. Every other canyon on Earth and even the Valles Marineris on Mars is compared to Grand Canyon. So how does Canyonlands and the rest of the canyon-y landscapes surrounding Moab stack up to Grand Canyon?

All canyons (e.g., deep valleys below towering walls found in arid and semiarid areas) are the result of fluvial erosion. That is, they are carved by rivers incising into high-elevation plateaus. Both Grand Canyon and southeastern Utah stand far above sea level. The South and North Rims of Grand Canyon are approximately 7,000 and 8,000 feet in elevation, while Moab itself sits at about 4,000 feet, and Deadhorse Point and the rims of Canyonlands are at approximately 6,000-6,400 feet. As a result, Grand Canyon is deeper than Canyonlands, reaching a maximum depth of about 6,000 feet versus the maximum of around 2,500 feet for Canyonlands.

On the other hand, Canyonlands is much wider than Grand Canyon. So wide that neither rim is in the national park. The east rim includes the Needles Overlook in Canyon Rims Recreation Area, and the Orange Cliffs of Glen Canyon National Recreation Area make the western rim. Rim-to-rim, Canyonlands ranges from about 21 to nearly 30 miles. Grand Canyon averages between 6 and 10 miles wide; the maximum is only 18 miles. Much of Canyonlands, particularly the Needles and Maze Districts, consists of smaller canyons set within the larger canyon beneath the much taller canyon rims.

Both Grand Canyon and greater Canyonlands region (including Arches National Park) have been carved by the Colorado River (and its tributaries) as it made its way to its outlet in the Gulf of California. Southeastern Utah contains two major rivers—the Green and the Colorado. They join in the heart of Canyonlands, 216 miles upstream of the start of Grand Canyon.

The Colorado River has a complex history as it evolved from ancestral rivers that did not flow to the sea. As the Colorado River reached toward the Gulf of California, its base level dropped, setting off waves of incision that swept upstream. As a result, the Grand Canyon is actually older than Canyonlands and Moab. Grand Canyon clocks in at about 6 million years old, but Canyonlands is younger, with most of its incision occurring within the last 2–3 million years.

The rocks exposed in Grand Canyon are also mostly older than the majority of those in southeastern Utah. Rocks in Grand Canyon range in age from 1,840 to 270 million years old. Here in southeastern Utah, they are between about 310 to 70 million years old.

Grand Canyon’s Coconino Sandstone, which is about 500 feet below the rim, is about the same age as the White Rim Sandstone in Canyonlands. Only the White Rim and layers (formations to geologists) below it, like the Cedar Mesa Sandstone in the Needles, overlap in age with the rocks of the top thousand feet of Grand Canyon. Rocks in the rest of the canyon’s depths are older. All rocks above the White Rim Sandstone, including almost all layers exposed in Arches, are younger than Grand Canyon’s rocks.

Having younger rocks has its benefits. When I worked at Grand Canyon, I used to joke that the canyon had “everything geologically except dinosaur fossils.” Grand Canyon doesn’t have dinosaur fossils because the rocks there are simply too old. The youngest was formed near the end of the Paleozoic (“ancient life”). With the exception of late Paleozoic rocks in the deepest canyons like in Canyonlands, Moab is dominated by Mesozoic rocks. The Mesozoic is better known as the Age of Dinosaurs. Dinosaur fossils (both bones and tracks) are found in several of the rock layers near Moab. Several world-class dinosaur localities such as the Mill Canyon Dinosaur Trackway and quarries in Utahraptor State Park are found here.

Grand Canyon is famous for having all three major types of rocks (igneous, metamorphic, and sedimentary), but so does southeastern Utah. The Moab area landscape is mostly made up sedimentary rock layers, but igneous rocks are found in the La Sal Mountains and metamorphic ones in Westwater Canyon north of Moab.

Moab has much more sandstone than Grand Canyon; so much so that Canyonlands could instead be known as Sandstonelands. Grand Canyon has some prominent sandstones like the Coconino. But the essence of Canyonlands emanates from sandstone. Sandstones, particularly massive ones like those found here, are scenery makers: they hold up sheer cliffs, make spires and needles, form curvaceous rock domes, and host arches, windows, and natural bridges. All features that the Moab area is particularly rich in.

Is Canyonlands better than Grand Canyon? That is up to you to decide since “better” results from a value judgement. But does Moab, Canyonlands, Arches, Dead Horse Point, and the rest of the area’s public lands have more than their share of geologic charms? I believe that this is something that we all can agree on.

A self-described “rock nerd,” Allyson Mathis is a geologist, informal geoscience educator and science writer living in Moab.
To learn more about Moab’s geology, visit the Geology Happenings archive online at https://www.moabhappenings.com/Archives/000archiveindex.htm#geology