MONTEREY PARK, Calif. - Law enforcement officials raided Hells Angels motorcycle gang hangouts across the West Wednesday and made 57 arrests after a two-year undercover investigation that netted illegal military explosives, guns and drugs.

Federal agents hit Hells Angels headquarters and clubhouses in Los Angeles, San Francisco, Arizona, Washington state, Nevada and Alaska before dawn.

Local authorities joined the California raids. Officials said Los Angeles was the hub of the investigation, but weren't more specific.

Federal agents made 40 arrests and California authorities took 17 people into custody. It was not immediately known if there were any arrests by local authorities in other states.

During the probe investigators offered to purchase explosives from members of the gang, said Donald R. Kincaid, special agent in charge of the Los Angeles office of the Bureau of Alcohol, Tobacco, Firearms and Explosives, at a news conference at the Los Angeles County Sheriff's Department.

"We purchased some stolen military explosives," he said, adding that they were identified as military property by lot numbers and other distinguishing marks.

Items seized in Los Angeles included about 50 firearms and a quarter-pound of suspected methamphetamine, bureau officials said. At least nine of those arrested on California charges were members of the San Fernando Valley chapter, including the president and three other officers.

"I just heard two gunshots … it just sounded like warning gunshots. Then I heard the reverberation of: 'Put your hands on the car,"' Catherine Robertson, who lives near the San Fernando Valley gang headquarters, told KABC-TV.

At the news conference, agents displayed motorcycle jackets, memorabilia and rifles, shotguns, semiautomatic weapons and pistols seized from the clubhouse.

Seventeen of the arrests were made in San Francisco, Richmond, San Jose and Santa Cruz County, said Marti McKee, a bureau spokeswoman in San Francisco. She declined to say what agents were looking for, saying the supporting documents were sealed by court order.

More information on the raids will be released "once we've determined the court documents have been unsealed," McKee said.

Agents arrested five people in Washington state at homes in Tacoma, Kirkland, Silverdale, Spokane and Wenatchee, said ATF spokeswoman Vera Fedorak in Seattle. Four arrests were made in Alaska, at three homes in Anchorage and one in Two Rivers.

Agents also searched clubhouses in Spokane and in Anchorage and North Pole, Alaska.

The arrests in Washington and Alaska were for drug trafficking, weapons charges, possession of stolen explosives and other crimes, Fedorak said.

Helmeted ATF agents raided the Hells Angels headquarters in Sparks, Nev., making one arrest and confiscating several items.

"This is just one part of a major operation going on throughout the day. Until that's concluded, everything we're doing is under seal and we really can't comment on it any further," agent Tom Cannon said.

One member of the club told KRNV-TV the agents took mostly clothing and trophies.

Seven arrests in Arizona included the president of the group's Tucson chapter, the former president of the Mesa chapter and other chapter leaders, the ATF said.