Along one rugged stretch of the Rio Grande, U.S. citizens routinely cross the border into the United States illegally. A shortage of basic services in rural Texas, such as health care, means U.S. citizens rely on Mexican services and rarely pass through an official port of entry on return.

Informal, unregulated crossings have been a fixture of life for generations in rural communities along the U.S.-Mexico border. Today, however, with the unrelenting focus on border security, this kind of unfettered back-and-forth by U.S. citizens is rare.

"We're citizens. We're U.S. citizens that have to go to get help in Mexico," said Loraine Tellez, a resident of the unincorporated town of Candelaria in West Texas. She said that the help principally involves health care.