Which is accurate about the Grand Canyon, in Arizona: The Coconino Sandstone that forms one of the prominent cliffs of the canyon is the youngest rock layer known from Arizona and surrounding states. The canyon is wider at the top and narrower at the bottom because the river was wider when the region was wetter, and has narrowed as deserts spread recently. A great thickness of sedimentary rocks exists in Death-Valley-type faulted basins, which can be seen deep in the canyon in many places. The oldest rocks are on top, with younger ones beneath, as shown by all of the footprints being upside-down in the rocks of the canyon walls. The rock record of the