CAMP PENDLETON, Calif. (AP) - A Marine has pleaded guilty to starting a brush fire that burned about 4,000 acres on the Camp Pendleton base and forced evacuations in Oceanside and Fallbrook last October.

Lance Cpl. Nason Lamb entered his plea during a court-martial Tuesday.

The 22-year-old Marine admitted he lit a clump of grass on fire with a cigarette lighter while he joked around with fellow Marines on Oct. 12.

He tried to stamp out the fire but it grew and merged with another wildfire.

An investigator says it cost $3.69 million to fight the blaze.

As part of a plea agreement, Lamb could be reduced in rank to private and receive a bad-conduct discharge when he is sentenced.

Copyright 2009 The Associated Press.