Bulldozers have begun plowing up ground at the mouth of Big Bend national park’s famed Santa Elena Canyon as part of the Trump administration’s multibillion-dollar “smart wall” expansion on the US-Mexico border, according to new footage taken by activists who have been monitoring the site.

Tensions have run high since the Trump administration announced plans to erect new border security infrastructure in the roughly 500-mile Big Bend region of south-west Texas, which includes the Lone Star State’s largest and most-visited national park.