TIJUANA, Mexico — In the northernmost corner of Mexico, where the United States’ southern border fence extends into the Pacific Ocean, dividing California from its truncated southern limb—the Baja California peninsula—binational seagulls dive for borderless fish.

Here, on either side of the rusty steel barrier that splits the beach between San Diego and Tijuana, separated families can meet along a swath of caged land called Friendship Park. They used to be able to embrace each other through the bars, but, in an effort to reinforce the fence further with steel mesh, that access has been progressively cut off.

The mesh serves no apparent purpose, other than to keep visitors from sticking their arms through the fence. But what once was a place that allowed hugging, is now a place for touching fingertips.