Geologic Formations. The Grand Canyon of the Colorado River is a world-renowned showplace of geology. Geologic studies in the park began with the work of John Strong Newberry in 1858, and continue today. Rock layers formed during the Paleozoic Era are the most conspicuous in the Grand Canyon’s walls. Coastal environments and several marine incursions from the west between 550 and 250 million years ago deposited sandstone, shale and limestone layers totaling 2,400 to 5,000 feet thick. Geologic Formations - Grand Canyon National Park (U.S. National Park Service)