A woman stands on the beach in Tijuana, Baja California, Mexico, as seen from Border Field State Park in Imperial Beach, California, through the fence marking the point at which the border between the United States and Mexico meets the Pacific Ocean.

A sign marks the border between the United States and Mexico on a bridge over the Rio Grande connecting Ciudad Juarez, Chihuahua, with El Paso, TX.

Children play on the playground of the Ignacio Zaragoza Primary School in Palomas, Chihuahua, Mexico. Behind them is the new fence marking the border with the United States.

Fernando Lerma, a volunteer with the Migrant Resource Center, siphons water through a hose while filling water tanks for thirsty migrants in the desert near Naco, Sonora, Mexico.

Mountains in the United States are seen from the Sonoran Desert in Mexico through the fence marking the border between the two countries.

A street scene in Nogales, Sonora, Mexico.

Two men climb over the fence separating the United States and Mexico in an attempt to cross into the United States illegally from Nogales, Sonora, Mexico.

A stray dog on the Tohono O'odham Native American reservation in Quijotoa, Arizona.

A new, stronger fence is under construction along the border between the United States and Mexico, as seen near Nogales, Sonora, Mexico.

A poster inside a shop window in Nogales, Arizona.

The border fence separating Mexico from the United States ends at the Pacific Ocean in Border Field State Park in Imperial Beach, California. On the other side of the fence is Tijuana, Baja California, Mexico.

A narrow path leads along the border fence between Mexico and the United States in Nogales, Sonora, Mexico.

A migrant from Honduras shows photos of his American son in Nogales, Sonora, Mexico. The man lived in Tennessee for years but was unable to begin the citizenship process by marrying his girlfriend because Tennessee does not recognize marriages by undocumented migrants.

An American flag flies behind a wall in Arizona City, Arizona.

Participants in a parade celebrating the annual rodeo and carnival on the Tohono O'odham Native American reservation swing their lassos in Sells, Arizona. The reservation in the rural Arizona desert is one of the most active areas for illegal immigration.

A view of the desert from Kitt Peak, Arizona.