Precambrian Basement Rocks
The basement rock formed 1.8 billion years ago when the North American continent collided with an ancient chain of volcanic islands, much like today’s Hawaiian Islands. Intense heat and pressure from the collision formed rock called Vishnu Schist. From deep under the earth’s surface, molten rock flowed up as magma between the cracks of the Vishnu Schist. As the flowing magma cooled and hardened, it formed veins of pinkish rock called Zoroaster Granite. Because of the extreme heat and pressure that folded and changed the rock, any fossils in the original rock were destroyed.
Bright Angel Shale
If you came to Grand Canyon area 515 million years ago when the Bright Angel Shale was forming, everything was covered by a very muddy, warm, shallow sea. Trilobites, brachiopods, crinoids and worm-like creatures that burrowed in the sea-floor thrived in the nutrient-rich water. This greenish-colored shale forms the broad, flat area known as the Tonto Platform in Grand Canyon.
Are you ready to go wading through the mud? About 280 million years ago the Grand Canyon area was covered by a broad coastal plain that had many slowly meandering streams. The environment was excellent habitat for an abundance of 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.
Have you ever wanted to visit the Sahara desert? About 275 million years ago the Grand Canyon area was covered with large dune-fields. The ocean lay to the west. 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 Grand Canyon. Cross-bedding (lines that run at steep angles to oneanother) can be seen in the rock, giving evidence to the wind-blown sand dunes that once covered the area.
About 270 million years ago North America was the western part of the super-continent Pangaea. The Grand Canyon region was once again covered by a shallow, warm, and well-lit clear sea with a sandy/muddy floor. Brachiopods, sponges, and other sea creatures dominated these waters. Other species included crinoids, corals, bryozoans, cephalopods, sharks and fish. This limestone is the youngest, and therefore the topmost, rock layer found at Grand Canyon National Park.