JACUMBA HOT SPRINGS, Calif. (AP) — On many nights, hundreds of migrants squeeze through poles in a border wall or climb over on metal ladders. They gather in a buffer zone between two walls with views of the night lights of Tijuana, Mexico, waiting hours for Border Patrol agents while volunteers deliver hot coffee, instant ramen and bandages for busted knees and swollen ankles.

About an hour drive east, where the moon offers the only light, up to hundreds more navigate a boulder-strewn desert looking for always-shifting areas where migrants congregate. Groups of just a few to dozens walk dirt trails and paved roads searching for agents.

The scenes are a daily reminder that San Diego became the busiest corridor for illegal crossings in April, according to U.S. figures, the fifth region to hold that distinction in two years in a sign of how quickly migration routes are changing.