Police in Tijuana said Sergio Ochoa Contreras, 32, a member of the La Familia cartel, had three .22-caliber rifles, a .410 shotgun and a third shotgun and 10 .22-caliber rounds in a Nissan Altima, SanDiegoRed.com reported.
Baja California police said in a statement Ochoa Contreras supplied weapons to the La Familia Michoacana cartel.
Police said Ochoa Contreras said he bought the weapons at a store named Best Sport in the United States, with help from his nephew, who lives in Bakersfield. The store's location was not provided.
The statement said Ochoa Contreras said for the past three months he had trafficked drugs, particularly marijuana, to the United States as a member of the La Familia cartel.
State authorities said they arrested five La Familia members in Tijuana Feb. 23 who had ammunition for AK-47s, cash and methamphetamine valued at $640,000.
The cartel has operated in the border region three years, authorities believe.
Weapons and ammunition used by criminal organizations are bought in stores in the United States and then smuggled into Mexico, authorities on both sides of the border say.