The concept of “national security” seems abstract in most of our political discussions, but there’s one place where the idea of the secure nation takes a concrete form: the US–Mexico border wall, a ragged concrete and steel barrier that cleaves the frontier and imposingly wards off outsiders. Lawmakers have long advocated further fortifying the border against unauthorized border crossings through more extended construction and militarized patrols.

Earlier this year, the debate over immigration reform led conservatives to propose a security plan that would fortify a 700-mile expanse of borderland with radar systems, surveillance cameras, “mobile automated targeting systems,” marine vessels to police the waterways, and unmanned aerial drones overhead. The entire apparatus — mostly concentrated in hotspots for border crossing, far from the Pacific edge of the wall — would be patrolled by some 40,000 border agents, aiming to apprehend, block, and deport as many unauthorized migrants as possible.

The parts of the border that take the form of an actual, physical barrier are an intrusion on the landscape, an eyesore to many — and to millions, a deadly obstacle to overcome. Elements of the local environment, from deserts to the Rio Grande, have been trampled, polluted, criss-crossed by truck convoys, occupied by federal agents and factories, and traversed by migrants following well-worn and perilous trails. And each phase of commercial development and economic exchange has also left an ecological mark, from the bustle of tourists to the churn of the maquilas to the  paths trod by migrants following smugglers.