PINE VALLEY, San Diego County — California legalizes marijuana for recreational use Monday, but that won’t stop federal agents from seizing the drug — even in tiny amounts — on busy freeways and backcountry highways.

Marijuana possession still will be prohibited at eight Border Patrol checkpoints in California, a reminder that state and federal laws collide when it comes to pot. The U.S. government classifies marijuana as a controlled substance, like heroin and LSD.

“Prior to Jan. 1, it’s going to be the same after Jan. 1, because nothing changed on our end,” said Ryan Yamasaki, an assistant chief of the Border Patrol’s San Diego sector. “If you’re a federal law enforcement agency, you uphold federal laws.”

The checkpoints, located up to 100 miles from Mexico, are considered a final line of defense against immigrants who elude agents at the border. They also have been a trap for U.S. citizens carrying drugs, even tiny bags of marijuana.

About 40 percent of pot seizures at Border Patrol checkpoints from fiscal years 2013 to 2016 were an ounce (28 grams) or less from U.S. citizens, according to a Government Accountability Office report last month. California’s new law allows anyone 21 and over to carry up to an ounce.

The Border Patrol operates 34 permanent checkpoints along the Mexican border and an additional 103 “tactical” stops, typically cones and signs that appear for brief periods.

Ronald Vitiello, acting deputy commissioner of parent agency Customs and Border Protection, called drug seizures an “ancillary effect” of enforcing immigration laws. Motorists typically are released after being photographed and fingerprinted. They generally aren’t charged with a crime because prosecutors consider them low priority.

State and federal marijuana laws have conflicted since California became the first to legalize marijuana for medical use in 1996. Next week, California will be among seven states and Washington, D.C., with legal recreational pot.

The government faces pushback over checkpoints. Some residents complain about delays and trespassers trying to circumvent checkpoints — some even dying from heat and exhaustion. Motorists who consider them a privacy invasion steadfastly refuse to answer questions and post their test encounters on YouTube.

Elliot Spagat is an Associated Press writer.