FRESNO — Federal and county law enforcement officers, who say the agricultural heartland of California increasingly is being used by people taking advantage of the state's medical marijuana laws, announced Wednesday that a summer-long crackdown has netted 73 arrests.

Officials with the U.S. Department of Justice and sheriff's officials from six counties announced the results of "Operation Mercury," a multi-agency effort to eradicate large marijuana growing operations from farmland.

Federal officials say operation has netted more than 120,000 plants, 32 guns and 1,500 pounds of processed marijuana.

Officials stressed they were not targeting people growing for legitimate medical need. They said many of the growers had large-scale operations that supplied dealers in other states.

As crackdowns on grows by Mexican cartels in Sierra wilderness areas have reduced activity there, they and other growers have taken advantage of California's medical marijuana laws in an attempt to move to San Joaquin Valley farmland, law enforcement officials said.

"These are large amounts cultivated for commercial purposes and sold to people often outside of California," U.S. Attorney Benjamin B. Wagner said.

When asked, officials did not know how much the regional crackdown on marijuana had cost, but they said they were targeting the large grows because of the criminal element they attract. Many grows are booby-trapped or protected by armed guards.

"As they infiltrate each and every county, it brings a criminal element," said Merced County Sheriff Mark Pazin. "If you use that as the central point you are bringing in the other riffraff. You're bringing in people hooked on this poison. Those are the unintended consequences of drug cartels coming in and procuring acreage in the breadbasket of America."

California, with its temperate weather, lax attitudes toward the plant and laws that allow growing and consumption for medical use, is home to most of the marijuana grown in the country.