What do Bess and Venters think about when they find human bone in the cliff dwellings?

When Bess and Venters find human bone in the cliff dwellings if gives them pause. It makes them think of these people, so long gone, and with no explanation of their demise. They wonder if they are heading for the same fate. It makes them think about their beautiful valley where they are so happy, but they know they must leave someday, or they may end up like the cliff dwellers.