Final answer:
The youngest rocks in the Grand Canyon are part of the Grand Canyon Supergroup, which includes various sedimentary units such as the Sixtymile Formation, Chuar Group, Nankoweap Formation, and Unkar Group. These rocks are above the Vishnu Schist and Zoroaster Granite and support the hypothesis that the Grand Canyon started to form around 5 million years ago.
Step-by-step explanation:
The youngest rocks in the Grand Canyon are part of the Grand Canyon Supergroup, which includes various sedimentary units. These rocks are located above the Vishnu Schist and Zoroaster Granite. They are represented by formations such as the Sixtymile Formation, Chuar Group, Nankoweap Formation, and Unkar Group.
These sedimentary units can be seen in the stratigraphic column of the Grand Canyon, where they are marked with a star. They consist of different types of rocks like mudstone, sandstone, and limestone.
The presence of these younger sedimentary rocks supports the hypothesis that the Grand Canyon started to form around 5 million years ago when the Colorado River began to cut through the stratigraphy.