The area north of Seligman is mostly private property or part of the Havasupia Reservation, which as far as I know is closed to travel without a permit. Other than doing some praire dog hunting off old Route 66 many years ago (with permission of the land owner), I've not had a lot of experiance with the area. I know there are several large sand stone quaries in the foothills to the north.
Geologically speaking off Old 66 are the Grand Canyon Caverns. It's a dry cave system. Haven't been there in years...