Going Backwards in Time: Layers of the Grand Canyon

As we reported in a recent post, adventure is a way of life for Hart Crowser staff. In January 2018, Geologist Kaelan Hendrickson also proved this by kayaking 226 miles through the Grand Canyon. He triumphed over numerous rapids, scrambled through side canyons, and endured winter conditions on the eleven-day trip. His goal: see and experience the tumultuous 1.8-billion-year geologic history for himself. The experience was like going backwards in time day by day.

Kaelan and the group of six began the adventure at Lee’s Ferry alongside the youngest layer of rock known as the Kaibab Limestone. This layer was formed 270 million years ago (give or take) by the sea that covered much of North America. After two days, they reached the next youngest rock layer, Coconino Sandstone. The mysterious cross-bedding throughout the layer was formed from dune fields much like the Sahara.

As the group descended into one of the darkest sections of the canyon, they reached the 280 million-year-old Hermit Shale layer, formed from low-energy streams. The landscape at this time was a coastal plain, tremendously different than now. Streams drained into the ocean and Permian reptiles roamed the plains. These streams carried fine particles that piled up over many years

The group continued going back in time, to the Supai Group layer, formed 300 million years ago from beach deposits. During this turbulent period, the coastlines changed rapidly: beaches, dunes, and shallow seas left rocks in their wake. An abundance of fossils are found in this layer.

Halfway through the trip, the group reached the Redwall Limestone, formed 340 million years ago when a shallow sea once again dominated North America. The rock here holds fossils of coral, brachiopods (marine animals that resemble clams), and other marine invertebrates. An uninformed traveler might think this layer was red all the way through, but the dramatic surface stain hides drab gray underneath.

Deer Creek Falls

Day 6: Deer Creek Falls flowing out of Redwall Limestone.

After a grueling eight days the group reached Bright Angel Shale, formed from a muddy shallow sea, much like the Mississippi River at the Gulf of Mexico. This layer holds shallow sea fossils such as crinoids (sea lilies and fans) and worms. The crinoid fossils can often be pulled intact straight out of the rock.

On day ten, the group finally reached the Precambrian Basement Rocks, the oldest rock in the Grand Canyon. The granites in this layer were formed 1.8 billion years ago by cooling underground magma. An island chain much like the Hawaiian Islands collided with North America, forcing magma to the earth’s surface. These rocks were under intense heat and pressure and are highly deformed. Today, they form the deepest part of the Grand Canyon including the infamous Lava Falls rapid, named for the lava-formed rock.

Once the group successfully navigated Lava Falls, they had kayaked down the largest rapid on the trip. While another day of paddling remained, the group had now seen 1.8 billion years of geologic history and conquered one of the most remote whitewater stretches in the United States. What they experienced will stick with them forever.

Grand Canyon

Day 8: Supai Group (top) through Bright Angel Shale (bottom).