CALEXICO, Calif. — A decade ago, when illegal immigration from Mexico was at a record high, this section of border was as good a place as any to sneak into the United States.
Migrants and smugglers could slip through the alfalfa fields outside town or plow their pickup trucks through the desert, where the biggest worries were stuck tires and getting safely across the irrigation canals.
But in the past five years, the international border here has become a harder, tougher, taller barrier — an American Great Wall. Miles of steel fencing now ride the desolate sand dunes west of Calexico, and to the east, Normandy barriers shaped like jacks block off old smuggling routes. The barriers are named for their resemblance to the defenses that lined the beaches of northern France in World War II.
Overall, the United States has added 413 miles of fencing to its southern boundary since 2006, raising to 649 miles the length of border that has some form of man-made barrier to people or vehicles. The Rio Grande creates a natural partition along another 1,252 miles, and the government has been putting new fencing there, too.
Now the question is: How much more should be built?
Border Patrol officials say their current plans are to construct just one more mile of fence, in Texas. But as illegal immigration takes an increasingly central role in Republican campaign debates, several GOP candidates have renewed calls to fence the entire 1,969-mile boundary.
President Obama has made light of such proposals, saying fence advocates won’t be satisfied until the United States builds a moat stocked with alligators. But leading Republican candidates Mitt Romney and Newt Gingrich have vowed to barricade the entire US-Mexico divide, with Gingrich signing a pledge to install a “double fence’’ while campaigning in Iowa earlier this month.
With such an endeavor projected to cost tens of billions of dollars, this stretch of California desert might be as good a place as any to assess how the existing border fence works.
The new barriers have been particularly effective at stopping vehicles from coming across, Border Patrol agents say. Along one stretch of desert here, the number of drive-through incursions plunged from 350 in 2007 to four so far this year.
But agents also say it is not the case that smugglers and illegal migrants on foot simply go to the place in the desert where the fence ends, and walk around it.
“Anywhere is a good place to sneak across if we’re not watching,’’ said Special Agent Jonathan Creiglow, a Border Patrol officer assigned to the agency’s El Centro sector here.
But there are also sections of 18-foot fencing right in the middle of downtown Calexico, opposite its sprawling sister city of Mexicali, where border jumpers can be up and over the wall in a matter of seconds, melting into shops and residential streets once they land on the other side.
At night, smugglers toss pot-stuffed footballs and fling golf-ball-sized heroin nuggets over to waiting receivers. Stealthy ultralight aircraft bomb the lettuce fields outside town with bundles of dope, then swoop back into Mexico, well below radar but high above the fence.
Then there are rugged sections in the desert where fencing is porous or nonexistent, but crossings rare. And those who do try to slip through are tracked by the Border Patrol’s array of sensors, night-vision cameras, and surveillance drones.
In short, agents say, fencing is a tool and a first line of defense, but it does not bestow border security by its mere existence. “Without the fencing we wouldn’t have as much time, but nothing is going to stop them from going over or cutting through it,’’ explained Creiglow, who, at 26, is one of the many recent hires at the Border Patrol, which has doubled in size since 2002, with 18,500 of its 21,500 agents now deployed along the US-Mexico frontier.