A fourth fire has sparked on Camp Pendleton, joining three others in burning more than 4,000 acres of the base.

The latest blaze started at about 5 p.m. Wednesday near Range 202 Whiskey Impact Area. Its quick spread forced crews from the Camp Pendleton and Orange County fire departments to perform an extended burn operation.

They worked through the night, clearing 1,100 acres around two training ranges.

Camp Pendleton fire officials say their work ensures Marines can come back to train without more fire risk and prevents the area from igniting later in the dry season.

Since Monday, three other fires began burning in live-fire impact areas and spread to about 4,000 acres.

A fire near North Basilone Road scorched about 1,100 acres as firefighters performed a hazard reduction burn.

However, none of the four fires are threatening structures or personnel, so Camp Pendleton fire officials are letting them burn out. Crews are staging in the area in case one gets out of control.

There is no word on when they expect the fires to be contained.