According to the article the petroglyphs were only worth between $500 and $1500 and so the question is why would anyone go to so much trouble for such a small amount of money?!! It's bad enough that someone would do this for any amount of money, but such a piddly sum? Not only is the crime reprehensible, but it's also just plain stupid!
According to the Times, the thieves used ladders, electric generators and power saws to steal the ancient art. The story says they “gouged holes in the rock and sheared off slabs that were up to 15 feet above ground and 2 feet high and wide.”
LINK: http://www.sierrawave.net/15279/petroglyph-story-spreads/