You may think that this is just graffiti but anything over 50 years old is protected by the Antiquities Act and should be preserved. We were later able to find one of these people and he told a neat story about how he and his college buddies happened upon the cave which at that time was really in the middle of nowhere. An interesting piece of cave history was saved. Many Grand Canyon caves have very dusty floors. This dust has accumulated over tens of thousands of years and contains pollen which may be studied to learn more about past climate.
Some caves there contain bones and other remains from animals that are now extinct.
Complete skeletons of a species of mountain goat have been found lying as if the animal died only 20 years ago instead of 10,000. Also split twig figurines dating as far back as 4000 years ago have been found in the same condition they were left. It is obvious that any mark we make on these caves will still be there long after we are gone. As another example, I have seen some very experienced and generally careful cavers groveling up a muddy slope only to drop into a white room. They proceeded through the room covering anything they touched with mud.