Three officers from U.S. Customs and Border Protection (CDP) met the group at the border, including port director Roque Casa and assistant directors Chris Leon (commercial operations) and Robert Schroeder (tactical operations). CBP is a law enforcement agency.

“Border security and anti-terrorism are the primary missions,” Casa said. “We deal in international commerce and it’s important to keep the movement of goods flowing across the border.”

CBP enforces laws and regulations for 400-plus government agencies, including USDA. CBP agricultural specialists keep a sharp lookout for prohibited foods and crop pests carried by passengers and their vehicles.

CDP processes about seven million passengers annually through a dozen lanes, including two million cars. The port is open round the clock.

No photos were allowed at the pedestrian crossing.

As the officers spoke, hundreds of people on foot wearing sweatshirts, scarves, and hats stood in the winter morning chill as the line moved slowly toward the border inspectors. Most of those crossing were men.

The words “Citrus Harvest” were stitched on one pedestrian’s backpack. Citrus is picked during the winter months in the Southern Arizona and California low deserts.

A dozen or so young children with backpacks waited in line. Caza says some children attend school in San Luis and further into Yuma County.

Up to 5,000 pedestrians cross the border from midnight to 8 a.m. during the busy vegetable and fruit harvest season.

According to the CBP website, the agency conducted about 25 million passenger inspections and 34 million cargo inspections at the nation’s 330 ports of entry during fiscal year 2011.

For agriculture, about 1.6 million quarantine materials were intercepted, mostly plant material and animal bi-products. There were 177,000 pest interceptions, including 50,000 cited violations.

CBP has about 2,300 agricultural specialists at 167 ports of entry.

At 8:00, the group boarded the bus and traveled to the nearby San Luis Port of Entry II where commercial traffic crosses the border in both directions.

Opened in 2010, the 80-acre port processes about 40,000 commercial trucks annually from 9 a.m. to 9 p.m. Officer Leon chuckled when he referred to the commercial port’s appearance with its “Jurassic Park”-type gates.”

During the winter months, about half of the trucks passing through the port transport produce. On site are representatives from the USDA, Food and Drug Administration, and veterinarians.

“Anytime we discover a pest in a farm commodity (shipment) we have a USDA person who identifies the pest as quickly as possible,” Officer Leon said.

About 75-80 percent of the commodities are X-rayed with a mobile machine which can inspect five trucks at a time. A permanent X-ray system is planned.

San Luis Port II is the only commercial port in the U.S. with a "cold room." If an importer has berries in the load and CBP wants to examine the commodity, the product is off loaded in the cold room.

“We will not jeopardize the commodity by bringing it to the dock and just have it sit there,” Leon said. “This way the importer knows the commodity is being well kept.”