At the end of a narrow and rutted road beyond the isolated Texan settlement of Candelaria, two concrete blocks separated by a river are just about all that is left of a once-thriving US-Mexico border culture.

Until recently, the blocks supported a footbridge that connected Candelaria with San Antonio del Río, the nearby Mexican village built on a desert flat at the foot of a chain of craggy mountains. The two communities helped pay for the bridge and it became a symbol of co-operation.