SAN DIEGO - Less than 20 miles south of San Diego, the flurry of city life gives way to the old rolling hills of southern California.
Wide open spaces stretch for miles, just north of the California - Mexico border. This is ground zero in the battle over illegal immigration.
The border fence here is actually two fences, a smaller, older fence made of interlocking metal called "landing mat" and a taller mesh metal fence with noticeable patches every few feet.
Border Patrol agents in this area say the holes were made by "cutters", cartel employees paid to pop over the smaller fence and cut holes in the taller one behind it, then quickly return to Mexico, before moving to another spot along the fence line and doing it all over again.
Smugglers try to exploit those holes to get either people or drugs into the U.S. illegally. It's part of the cat and mouse game that plays out between agents and smugglers 24-7.
Further east, the fencing changes again. Closer to the desert, 18-foot steel posts are used. This is called "bollard fencing".
Agents prefer to call all of it "infrastructure" and say it gives them more time to respond to an incident, react to a threat or bring in additional agents to assist. Apprehensions in this area are up 33% compared to last year. The job is tough and dangerous and comes with more criticism than most.
Agents here say, they want the public's support and their greatest challenge right now is making Americans understand why their work is important.
They say better border security has led to an economic boom in southern California. Developers now willing to invest big bucks to build on land that used to be considered no man's land because of the sheer number of border crossers using it to come into the US.