Favorite Layers of Grand Canyon: Rangers and Guides Pick Their Rock

Episode 21 of Behind the Scenery, the podcast of Grand Canyon National Park's North Rim interpretation team, first posted December 28, 2021.

"Favorite Layers of Grand Canyon." NPS.

Geology shapes every part of the human experience of Grand Canyon. In this episode, rangers Ceili and Kate — recording at the bottom of the canyon, among the Vishnu Schist and Zoroaster Granite — answer visitors' favourite geology questions, then ask colleagues and friends which rock layer they love most.

Three-Mile Resthouse on the Bright Angel Trail. NPS / M. Quinn.

What visitors ask

• "What's the green rock?" The Bright Angel Shale. It is green from glauconite, a mineral that forms where its sediment was laid down in a shallow sea. It is rich in fossils: worm tracks and burrows, and trilobite tracks are found regularly.
• "How old is this?" Very old — and some older than others. The youngest rocks, at the top, are 270 million years old; the oldest, at the bottom, between 1.8 and 1.6 billion.
• "Are there dinosaurs?" No: the layers are older than the dinosaurs. The top layer has sharks and shark teeth; elsewhere there are trilobites, shells, plants such as ferns, and tracks of animals older than what we think of as reptiles.
• "Are these the same rocks as Zion?" No — but the bottom layer at Zion is the top layer at Grand Canyon. Zion sits on top of Grand Canyon in the Grand Staircase, which can be seen whole from parts of the Kaibab Plateau.

On the trail, the questions are usually about the next water station, blisters and getting out alive — but those too come down to geology, which governs a hiker's whole day.

Favourite layers

Inspired by long evening talks on the porch at Phantom Ranch, the hosts asked around:

• Coconino Sandstone — Ranger Doug, North Rim seasonal ranger. It is so distinctive that he points it out at visitor centres; from the North Rim Lodge he can see where the Bright Angel Fault offsets it, a landmark for the Bright Angel Trail and the village.
• Coconino Sandstone — Matthew Baldwin, backcountry office. Its big white cross-bedded cliffs mean you are almost home on the hike out. He once lost a green hat off a cliff in a blizzard near the South Kaibab Trail — if you see it, bring it back.
• Esplanade — Jen, who estimates she has hiked something like 20,000 miles below the rim. It feels like another planet, like walking on Mars, and speaks of the people who once lived on it. It is not easy walking: avoiding the fragile cryptobiotic soil means constant sidestepping and scrambling.
• Redwall Limestone — Michael Wichman, a backcountry guide of 13 years. It has the most caves, where condors roost and fledge; it can be 1,000 feet thick; and waterfalls tend to spring from its base where water hits the impermeable Bright Angel Shale. His second pick, the Chuar formation near Lava Chuar Canyon, is teal and turquoise with wavy U-shaped features, seen only in that area.
• Redwall and Muav Limestones — Jesse Barden, North Rim interpretation supervisor. Together they hold the best caves and slot canyons, and most major springs flow from the Muav. He recalls climbing the Red Slide Route through the Redwall with a friend on a January river trip — a route description of a few sentences that never mentioned the unprotected climbs up cliff bands, one of them 15 feet high, with heavy packs.
• Bright Angel Shale — Jeff Caton, North Rim lead interpreter. He likes the way it crunches under his boots — and remembers that crunch from a backpacking trip where he ignored the rangers' advice, fell ill and knelt on it to be sick.
• Tapeats Sandstone — Elyssa Shalla, park ranger. Touching its sediments carries you back through the canyon's ancient landscapes; she remembers years at Indian Garden and the Tapeats Narrows, "packed with beauty and suffering."

Sources

• National Park Service, Grand Canyon National Park, North Rim Interpretation, "Behind the Scenery Podcast #21 — Favorite Layers of Grand Canyon," December 28, 2021. https://www.nps.gov/articles/000/behind-the-scenery-podcast-favorite-layers-of-grand-canyon.htm
• More episodes: https://www.nps.gov/podcasts/behind-the-scenery.htm
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.