NOGALES, Arizona (CNN) -- Nogales, Arizona, is a small city. Just more than 20,000 people live here, according to the 2005 census. But spend a couple of days here with law enforcement, and your head will spin.
Almost half of all illegal drugs seized from Mexico last year were seized in the eastern Arizona region, and Nogales is the largest border city in this U.S. border patrol sector.
In the past six months, the Border Patrol has seized about 500,000 pounds of illegal drugs here, which is 15 percent higher than the previous six months. Each day, hundreds of people are arrested, mostly for immigration violations but many for drug and weapons crimes. The temporary jail cells in the Border Patrol station in Nogales are often overflowing. The Border Patrol boss in this sector says his agents were assaulted 260 times within the past year.
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One night this week, we saw the danger and variety of lawbreaking activity experienced here quite vividly.
At the immigration checkpoint set up a half-hour north of Nogales on Interstate 19, a semi truck is pulled over when the drug-sniffing dog detects something. The back of the truck is opened, and inside are thousands of tomatoes, but the dog is still not happy.
The truck is taken back to the Border Patrol station, and agents climb over the tomatoes. And that's where they find the stash. Bales and bales of dope. Forty bales of marijuana. Nine hundred eight pounds, to be exact. At a street value of $800 a pound, the authorities estimate they kept $720,000 worth of marijuana off the streets.
I interview the man arrested for driving the shipment. The operating theory: that he is doing dirty work for one of the Mexican cartels. But the Mexican man tells me he is not scared, because "I was just carrying tomatoes." He claims that he knew nothing about the nearly half-ton of pot. The man will be telling that to the judge and could face significant time in an American prison.
Illegal drugs consume the day of all law enforcement people here.
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We drive with the Border Patrol in the late hours of the night and hear a call over the radio that two men have been spotted jumping the border wall with backpacks.
The chase is on, and another dog is brought to the area. The men disappear, but the dog picks up a scent in the heavy, hilly brush. Sarah the drug-sniffing dog is taught to sit when she finds something.
She suddenly sits and then jumps on what looks like bushes. It turns out the bushes are actually attached to sacks of marijuana. Two 25-pound sacks full of pot.
They were abandoned by the men when they ran away after being spotted. Street value, at least $40,000.
Ray Rivera, the agent who works with Sarah, told me that over the past two years, Sarah has found nearly 7,000 pounds of pot. But Rivera also is pretty heroic. Just a couple of weeks ago, he was shot in the leg when a man he was chasing committed suicide. The bullet passed through the man's face and into Rivera's knee. Law enforcement life here is not for the squeamish.
Before we leave this area, we go to a rural area west of Nogales where we hear illegal immigrants and drug couriers often try to get into the United States. When we get there, we see why. The tall border fence abruptly ends as it gets close to a small mountain, but there is plenty of space for people to squeeze into the United States.
We wander about 10 feet into Mexico to look at some of the clothes, water bottles and cigarette boxes that people have left behind. As we get ready to leave, we see a Border Patrol vehicle zooming towards us. They don't know we're with CNN; they think we may be criminals.
One of the four agents points his rifle at us and demands that we keep our hands in plain sight. They search our car, and we tell them who we are and what we're doing. They say they spotted us because of their long-range video cameras. They tell us to give them a heads up next time we go exploring, and all is well.
The agents did their job well. But there are only so many of them and an immense amount of border. After spending time with these agents, it's easy to see how sometimes what they do feels like a thankless task.
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ed up over there. Mexican five-oh just arrested the 2nd biggest cartel runner in Mexico City while the dude was out for a jog and they keep finding abandoned cars full of weapons and drugs across the river. I saw on the news that we're asking for more resources and back up incase this shit starts to spill over really bad. 
