The prison that houses some of California's most violent inmates will remain on lockdown for several weeks as authorities investigate what they call a "very sophisticated" plot to kill three guards.

Pelican Bay State Prison (search) has been under a state of emergency since Feb. 4, when inmates alerted prison officials to the plot, spokesman Lt. Steven Perez said Saturday. He said investigators believe the plot was orchestrated by members of the Mexican Mafia (search), a well-organized prison gang.

"There is no doubt in our mind that this plot, had we not uncovered it, very well may have succeeded," Perez said. "It was a very sophisticated plot, and our concern is that we could have lost lives."

All 1,400 general population prisoners have been confined to their cells since Feb. 4 as guards search cells and interview inmates.

Guards have found about a half dozen weapons they believe are connected to the plot but believe there are up to 10 that have yet to be discovered, Perez said.

Perez wouldn't say exactly what types of weapons were uncovered but described them as "typical inmate-manufactured weapons." Such weapons can include pieces of metal filed into a knife, or plastic bottles or toothbrushes that are melted and rolled to a spearlike point. Metal filings or prison-issued razor blades are sometimes inserted while the plastic is softened.

Five or six inmates have been segregated for further questioning, Perez said.

Pelican Bay, about 20 miles south of the Oregon border, is home to some of the state's most hardened criminals, most of whom are serving lengthy terms for violent crimes.