The Grand Canyon tells one of the world’s greatest geologic stories. The beginning of the story starts at the bottom of the canyon and moves forward in time as you get closer to the rim. Imagine a stack of pancakes, where the oldest is at the bottom, and the newest is on the top! It’s the same with layers of rock.
There are distinct horizontal layers of different rocks in the canyon that provide information about where, when, and how they were deposited, long before the canyon was even carved. In conjunction with layers of rock types, fossils also give us a snapshot of past plant and animal life.
The three main types of sedimentary rocks at Grand Canyon are sandstone, shale (or mudstone), and limestone.
If you’re interested in learning more, visit the Trail of Time in Grand Canyon National Park. This 2.8-mile paved walk allows guests to touch the rock layers as they move through the canyon’s geological history.
If you came to the Grand Canyon area 515 million years ago when the Bright Angel Shale was forming, everything was covered by a very muddy, warm, shallow sea. This greenish-colored shale forms the broad, flat area known as the Tonto Platform in the Grand Canyon.
About 280 million years ago the Grand Canyon area was covered by a broad coastal plain that had many slow, meandering streams. The environment was excellent for ferns and conifers, along with reptiles and insects, including dragonflies with 12-inch wingspans. This layer consists of siltstones, mudstones, and fine-grained sandstones rich in iron that create a gentle, red slope in most parts of Grand Canyon National Park.
About 275 million years ago the Grand Canyon area was covered with large dune-fields. Reptiles, spiders, scorpions, and other insects dwelled on the sand dunes of this extensive desert, leaving their tracks fossilized in the sandstone. This sandstone layer creates a broad, light-colored cliff a few hundred feet below the rim of the Grand Canyon.
About 270 million years ago North America was the western part of the supercontinent Pangaea. The Grand Canyon region was once again covered by a shallow, warm, and well-lit clear sea with a sandy floor. Sea creatures dominated these waters including sponges, corals, bryozoans, cephalopods, sharks, and fish. This limestone is the youngest, and therefore the top-most, rock layer found at Grand Canyon National Park!