Like many people in the tiny town of Why, Ariz., Stephanie Fierro’s life revolves around the nearby border crossing. She works at a roadside café serving enchiladas to American tourists passing through on their way to beach resorts in Mexico. Her husband, a Mexican citizen, lives on the other side.

That link was severed last week when United States border officials closed the port of entry in nearby Lukeville, Ariz., to cope with an influx of thousands of migrants who have been camping out in a rugged patch of desert along the border wall. Border officials have said they had to close the port to legal crossings in order to focus all their resources on the surge of unlawful crossings.

It has created a split-screen crisis — a humanitarian emergency at the border, where hundreds of migrants are burning cactuses and trash to keep warm at night, and an economic disaster for people in rural southern Arizona whose lives and livelihoods depend on the now-shuttered border crossing.

“We come and go every day,” said Ms. Fierro, 26, who is eight months pregnant with her second child. If the border stays closed, she said, she doubts she will be able to see her husband before her due date. “That’s just wrong.”

Without the traffic from the roughly 3,000 people who cross legally into the United States daily in Lukeville, gas stations, restaurants and travel-insurance agencies farther up the road that cater to passing tourists said their business had dropped by 90 percent.

Mexican American families who work in Arizona but live just over the border in Sonoyta, Mexico, are scrambling to figure out how to get their children to school, commute to work, or care for parents they can no longer easily visit.