In the 1980s, when Kevin Dahl first began visiting the Organ Pipe Cactus national monument in southern Arizona, the border was unmarked, save for a simple fence used to keep cattle from a ranch in the US from crossing into Mexico. In those days, park rangers would call in their lunch orders at a diner located just across the border. Since then, a 30ft steel bollard wall has replaced the old barbed wire fence at Organ Pipe.