Those snakes are in their hibernaculum, where they spend the winter for the very reasons you mention. They can avoid extreme temps. There is no reason to kill those snakes, and most of your snake bite victims out there get bit because they are trying to f*** with a snake that just wants to be left alone. If you really want to move those snakes, without killing them or injuring them, which gasoline and all the other methods will do, contact your local herp society.
Phoenix Herpetological Society Get a hold of the president, chances are s/he will know a crazy member that is good at safely handling rattlesnakes and that will have a good time playing with those rattlesnakes while you are busy digging. This person or persons might just do it for fun because, believe it or not, some of us go looking for snakes on purpose and all we take is a photo. Barring that offer to pay him. If you're willing to risk that hike and being killed by snake bite, $100 doesn't seem like that big of a downpayment on the Beale Treasure or whatever you're looking for.
