More than 578,000 cannabis plants, worth over $1 billion, have been uprooted from forests and national parks in a major operation in the western United States, the Justice Department said.

The two-month enforcement operation, which began July 1 in seven states -- California, Arizona, Idaho, Nevada, Oregon, Utah and Washington -- was led by the nation's anti-drug and forest authorities.

"Federal, state and local law enforcement in the seven states have eradicated more than 578,000 marijuana plants from public lands. The DEA estimates the value of this marijuana to be well over $1 billion," the Justice Department statement said.

Most of the illegal plantations were discovered in California, where "at least 484,000 marijuana plants" were seized in over 96 fields.

"Huge amounts of trash, miles of irrigation line, and many pounds of fertilizer and pesticides were removed from grow sites on public lands," the department said. Weapons were also found.

Fourteen people were arrested and charged in the Eastern District of California in connection with the illegal crops.

Still, forests and national parks continue to suffer "the effects of illegal marijuana ... long after the crop is harvested. Marijuana growers remove natural vegetation to make room for the marijuana. They cut down trees to allow sunlight into the site, and they divert streams from their natural path to irrigate the land," the statement said.