SACRAMENTO, Calif. (AP) — Federal authorities in California vowed to shut down dozens of pot growing and sales operations in a major crackdown, saying the worst offenders are using the cover of medical marijuana to act as storefront drug dealers. The aggressive crackdown comes a little more than two months after the Obama administration toughened its stand on medical marijuana. Prosecutors Friday described it as the first coordinated statewide offensive against marijuana dealers and suppliers who use California’s 15-year-old medical marijuana law as legal cover for running sophisticated drug trafficking ventures in plain sight.