how did this form?
By deposition  in warm, shallow seas and near ancient, long-gone sea shores in western North America.
Geology of the Grand Canyon area
The geology of the Grand Canyon area includes one of the most complete and studied sequences of rock on Earth. The nearly 40 major sedimentary rock layers exposed in the Grand Canyon and in the Grand Canyon National Park area range in age from about 200 million to nearly 2 billion years old. Most were deposited in warm, shallow seas and near ancient, long-gone sea shores in western North America. Both marine and terrestrial sediments are represented, including lithified sand dunes from an extinct desert. There are at least 14 known unconformities in the geologic record found in the Grand Canyon.

what is the second layer of the grand canyon made of It is made up of nearly 40 major sedimentary rock layers how many layers are there? 40 layers
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Geology of the Grand Canyon area [SEP] Introduction
The new river captured the older drainage to form the ancestral Colorado River, which in turn started to form the Grand Canyon. Wetter climates brought upon by ice ages starting 2 million years ago greatly increased excavation of the Grand Canyon, which was nearly as deep as it is now, 1.2 million years ago. Volcanic activity deposited lava over the area 1.8 million to 500,000 years ago. At least 13 lava dams blocked the Colorado River, forming lakes that were up to deep. The end of the last ice age and subsequent human activity has greatly reduced the ability of the Colorado River to excavate the canyon.