Part iii the grand canyon is one of the most spectacular laboratories of historical geology in the world. use the cross section of the eastern grand canyon (next page) to answer the following questions. 1. what is the oldest body of rock in the canyon? 2. what is the youngest pre-cambrian formation in the canyon? 3. what formations comprise the cambrian system in this area? 4. what does the sequencing of the cambrian system tell us about sea level changes during this time? 5. what was happening geologically in the canyon during the ordovician period? 6. which rock formations are indicative of the regression of the oceans? (oceans retreating from the continents).