On the other side, visible through the gaps in the towering barrier, a group of more than 100 people – from countries including Ecuador, Colombia, China and Rwanda – huddled together, waiting to be let through on to US soil. This border point south of San Diego is now one of the busiest along the entire US-Mexico frontier, which stretches around 1,950 miles (3,140km) from here to eastern Texas and the Gulf of Mexico.