Enough people were caught trying to illegally cross the border from Mexico to California in 1996 to outnumber the population of the city of Sacramento. But last year, the number of California border apprehensions wouldn't even fill the small town of Lincoln.
Border Patrol agents apprehended about 39,000 people trying to illegally cross the California border from Mexico in 2015, down by 510,000, or 93 percent, from 1996, according to the latest data from the U.S. Department of Homeland Security.
Border Patrol figures are often used as an indicator of how many immigrants are trying to cross the border illegally. A few things help explain the decline:
• Illegal immigration is down everywhere along the Mexican border. The recession that began in 2007 also corresponded with a sharp reduction in migration from Mexico. Put simply, why come here if there are few jobs? Immigration has not yet returned to old levels.
• Increased enforcement. The number of border patrol agents nationwide has tripled since 1996, federal data show. More agents can mean more trouble illegally crossing the border.
• A shift east. The federal government beefed up enforcement near San Diego during a controversial, mid-1990s program called Operation Gatekeeper. The operation, along with the high cost of living in much of California, pushed illegal immigration to weaker points east along the border - a trend that continues. Last year, the Border Patrol apprehended almost six times as many immigrants at the Texas border as they did at the California border.
As a result of these and other trends, more Mexicans are leaving the United States than coming here, according to the Pew Research Center.
This map shows U.S. Border Patrol apprehensions by field office in the southwest in 1996 and 2015.