1) If an outcrop shows alternating layers of sandstone and limestone, what can you assume about the geologic history of that region? I said that the region had alternating periods of arid desert / dune-covered beach (sandstone layers) and shallow sea (limestone layers), am I correct? I know that limestone indicates that it was deposited when the region had a shallow sea, but I am not too sure about the sandstone part, are sandstone layers usually formed in arid desert / dune-covered beach? "Some light-colored layers in the Grand Canyon are composed of sandstone. Someo f these sandstone layers show cross-bedding, which is characteristic of sand dunes. Therefore, it appears that these layers were laid down when the region was either an arid desert or a dune-covered beach. The layers of limestone and shale must have been deposited when the region was covered by a shallow sea." (quote from textbook) This quote makes me to think that only sandstone with cross-bedding can be assumed to be formed in desert / beach environment, but those sandstone without cross-bedding can't be assumed this way...and this leads to my uncertainty above 2) From the above quote, what can you tell about the history of the Colorado Plateau? I can't figure out this as well...can someone explain? Thanks a lot! Please Register or Log in to view the hidden image!