You know that the road would violate your rental agreement and you'd still consider it?
I really don't think you appreciate the disaster that is driving in violation of a rental agreement. First of all, all rentals these days have gps tracking so they will know you broke your contract. Breaking your contract basically means you are driving a stolen car, and will invalidate any insurance you have, so any problems that do happen will completely come out of your pocket. That means if you cause a mechanical problem by driving on that road, you could be completely responsible for having the vehicle towed (potentially all the way back to Vegas), be liable to pay for any and all damages/repairs, and the lost time where it can't be rented to anyone else.
Basically, you'd be taking a gamble that could easily end up costing you thousands upon thousands of dollars.