 The Grand Canyon is a geologic museum of epic proportions. Of the earth’s 4.6-billion-year history, nearly half is put on display in the canyon. If you were to hike one of the trails leading to the Inner Gorge, you would be able to see exposed rock strata ranging in age from 1.7 billion years at the Inner Gorge, to limestone deposited 250 million years ago on the Kaibab Plateau, to the 1-million-year-old black lava flows in the western canyon. It took the Colorado River a mere 4 to 6 million years to cut through these rock layers to create the Grand Canyon.
 The bulk of the rock formations seen in the canyon are sedimentary, having been created as the result of marine and river deposits and tall sand dunes. The youngest of the rock formations were formed by volcanoes.After the Pacific continent plate crashed into the the North American plate and created the Rockies, the Colorado River began its mighty work. As the sediment-laden Colorado proceeded to its new outlet in the Gulf of California, it deepened and widened the canyon to a present 18 miles in places with the help of wind, rain, ice, and gravity.
- Kaibab Limestone: formed 245 to 260 million years ago, highly fossilized, buff colored, caps the rim
- Toroweap Formation: formed 245 to 260 million years ago, formed by calcareous deposits of creatures living in the sea
- Coconino Sandstone: formed 260 million years ago, remnant of a period of desertification when the area was covered by huge sand dunes, swirling and white
- Hermit Shale: formed 270 million years ago, formed by mud and silt deposits like the present day Mississippi River, red slopes
- Supai Group: formed approximately 300 million years ago, sands and mud deposited by rivers to near ocean shores, ledges and slopes
- Surprise Canyon Formation: formed 335 million years ago, formed when a river valley flooded and became a swamp
- Redwall Limestone: formed 340 million years ago, formed by calcareous deposits from creatures living in a tropical sea, unbroken rose-colored cliffs
- Temple Butte Limestone: formed 375 million years ago, calcareous deposits from marine creatures, purplish and gnarled
- Muav Limestone: formed 520 million years ago, formed by marine creatures that lived in warm aters of the tropical, Caribbeanlike sea as it made its way east
- Bright Angel Shale: formed 540 million years ago, mud and silts left as sea moved eastward, shales evidence of deep and calm waters, purple and green
- Tapeats Sandstone: formed 560 million years ago, formed as mountains worn down and sea moved inland, ancient beach sand, dark brown
- Vishnu Schist: formed almost 2 billion years ago, formed when the collision of two continents pushed up a mountain range 5 to 6 miles high
- Zoroaster Granite: formed almost 2 billion years ago, cooled and hardened remains of once molten rock, found in the black schist, stripes of pink.
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