Children walk across the U.S.-Mexico border with crystal methamphetamine strapped to their backs or concealed between notebook pages. Motorists disguise liquid methamphetamine in tequila bottles, windshield washer containers and gas tanks.

Methamphetamine smuggling at land border crossings has jumped in recent years but especially at San Diego's San Ysidro port of entry.

The Western hemisphere's busiest land border crossing accounted for more than 40 percent of methamphetamine seizures in fiscal year 2012. That's more than three times the second-highest — five miles east — and more than five times the third-highest, in Nogales, Ariz.

The spike reflects a shift in methamphetamine production to Mexico after a U.S. crackdown on domestic labs and the Sinaloa cartel's new hold on the prized Tijuana-San Diego smuggling corridor.