PINE VALLEY, Calif. — 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.

STATE PERMITS 1 OUNCE OF POT

About 40 percent of pot seizures at Border Patrol checkpoints from fiscal years 2013 to 2016 were an ounce 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.

The clash between state and federal laws played out on a smaller scale near the Canadian border in Washington after that state legalized marijuana in 2014. California is a far busier route for illegal crossings with many more agents.

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. Maine voters have approved recreational marijuana, and lawmakers are working on legislation to implement sales of the drug.

SESSIONS SIGNALS HARDER STANCE

U.S. Attorney General Jeff Sessions, a staunch opponent of legalization, said last month that he was taking a close look at federal enforcement, suggesting a tougher stance than President Barack Obama’s administration.

At highway checkpoints, Border Patrol agents look for signs of nervous drivers, like clutching steering wheels and avoiding eye contact and interrupting when passengers are asked to state citizenship. Some panicked drivers make a U-turn when they spot the checkpoint, a dead giveaway.

The U.S. Supreme Court ruled in 1976 that agents can question people at checkpoints even without reason to believe anyone in the vehicle is in the country illegally and don’t need a search warrant.

Michael Chernis, an attorney who represents people charged with marijuana crimes, believes checkpoint seizures are a waste of resources but acknowledged the government is empowered.

“The bottom line is, there’s absolutely no protection against federal interaction when it comes to adult use,” he said.