) Physical map for the western U. S. labelled, Western United States map. The map includes the Mississippi River on the eastern side of the map and the Pacific Ocean on the western side of the map. The Rocky Mountains run through the center of the western part of the map. West of the Rocky Mountains the area is brown. East of the Rocky Mountains the area is green. Unlabled rivers run through the entire map. Using the map and your knowledge of U. S. history, what do the details of the Rocky Mountains suggest about the Lewis and Clark expedition? The group made a grave mistake in not turning back in Missouri. The group really could have traveled by river all the way to the west coast. The group would have been better off traveling by horseback the entire journey. The group most definitely needed a guide to find the easiest route through the mountains.