Close to the southern tip of Texas, a border wall suddenly ends. Its final post sits in a dry cornfield half a mile from the nearest bend in the Rio Grande river, the actual border with Mexico.
It would be easy to walk around it. Tires left by the border patrol rest nearby. Agents drag them behind trucks to smooth the cracked earth and check for footprints.
Unlike famous barriers such as the Berlin Wall or the Great Wall of China, the US version is not much of a wall. What stands in Texas is a fragmented series of fencing, composed of enormous steel bars embedded in concrete close together. The rust-colored thick bars that must reach a height of 18ft loom over the landscape, forming teeth-like slats that split farmland, slice through backyards, and sever parks and nature preserves.
There are miles of gaps between segments and openings in the fence itself. As a result of the Secure Fence Act passed in 2006, the government built some 650 miles of wall along the 1,954-mile US-Mexico boundary. While 1,254 miles of that border is in Texas, the state has only some 100 miles of wall.
Republican presidential candidates insist they will finish it. But completing the Texas part of the wall would be a daunting task, thanks to the border’s sheer length, the fact that it sits in the center of the snaking Rio Grande, and because treaties with Mexico prevent either country from constructing within the river’s flood plains. And unlike in other south-western states, most border land in Texas is privately owned.
Finishing the some 1,300 miles of border fencing would also be costly. According to a 2009 government accountability report, pedestrian fencing, meant to keep out smugglers and migrants crossing on foot, has run anywhere from $400,000 to $15.1m per mile, averaging $3.9m.
More recent construction has been even more expensive, with segments constructed in 2008 costing $6.5m per mile. If kept at this rate, the wall would cost nearly $10bn to complete just for materials, and challenging geography could bring it much higher.
“With every twist and turn of the Rio Grande and every steep terrain in Arizona, it would cost easily that much,” said Adam Isacson, a border expert for the Washington Office on Latin America.