Just an aside about the vandalism issues.
We have a friend here in Las Vegas who is part of a national "posse" of people tasked with safeguarding petroglyphs and pictographs in the Mojave Desert. Each member is responsible for one specific art installation and they are sworn to keep the location secret. They even agree not to tell their spouses or close friends the location. Once a month, depending on weather, they drive/hike to their "art" and check on the condition. They are allowed to tell someone that they are heading out there and given a rough GPS location, in case they don't return on time.
This posse currently has an inventory that is reputed to number in the hundreds. I personally know of a dozen places that are not listed on any map and most are within an hour or two of Las Vegas. In some places in the Mojave, I doubt it is possible to walk more than 30 minutes in any direction and not find more examples of this ancient graffiti. One such place is an about hour from my house and it is a place where kids (boys) have been going for millennia for practice shooting. In the parking area (wide spot in the road), it is possible to find .22 shells and arrowheads in close proximity.
In the near-by Red Rock Canyon National Conservation Area, are a very number of petroglyphs who routinely get hit by spray can-wielding assbites. Local volunteers have formed a team of dedicated cleaners who are proficient at removing modern graffiti while not damaging (too much) the underlying rock art. I have some representative photos someplace. I will try and find them and post here.
In the meantime, here is a Mountain Sheep (possible depiction) found in Sloan Canyon about 30 minutes from my house.
Photo by Deborah Wall, published in Base Camp Las Vegas: 101 Hikes in the Southwest.
Mark