SAN DIEGO — Federal prosecutors in the Southern District of California filed 75 border-related cases this week, charging defendants with fentanyl importation, illegal re-entry after deportation, and smuggling aliens for financial gain along the 140-mile border the district shares with Mexico.

The caseload underscores the district’s status as the fourth-busiest federal jurisdiction in the country, driven by its proximity to the San Ysidro Port of Entry — the world’s busiest land border crossing — connecting San Diego, America’s eighth-largest city, and Tijuana, Mexico’s second-largest city.

Among those arrested was Ana Sanchez, a United States citizen, who was taken into custody on June 6 and charged with importation of a controlled substance. Customs and Border Protection officers at the San Ysidro Port of Entry discovered 31 pounds of fentanyl and 21 pounds of another substance hidden in the seats and quarter panels of her car, according to a criminal complaint. Sanchez was previously convicted of the federal offense of importing drugs into the Southern District in 2018.

On June 9, Carlos Nunez-Valdivia, a Mexican national, was arrested and charged with attempted entry after deportation at the Otay Mesa Port of Entry. According to the complaint, Nunez-Valdivia applied for admission by falsely claiming to be a lawful permanent resident. He has been previously deported at least three times.

The same day, Victor Manuel Garcia-Ramirez, a United States citizen, was arrested and charged with bringing in aliens for financial gain. Garcia-Ramirez attempted to smuggle two undocumented Chinese nationals into the United States at the San Ysidro Port of Entry inside a non-factory compartment built beneath the undercarriage of a Nissan Armada, according to the complaint.

The cases were referred or supported by Homeland Security Investigations, ICE Enforcement and Removal Operations, Customs and Border Protection, U.S. Border Patrol, the Drug Enforcement Administration, the FBI, the U.S. Marshals Service, and the Bureau of Alcohol, Tobacco, Firearms and Explosives, along with state and local law enforcement partners.

All defendants are presumed innocent until proven guilty. Initial court appearances in the Southern District of California are expected in the coming days.