RANCHO SAN DIEGO, Calif. -- Another 21-member contingent of state firefighters based in San Diego County departed Tuesday to help battle a conflagration raging in Northern California.

The firefighters left Cal Fire's San Diego County headquarters near El Cajon aboard a chartered bus in the late morning, said Nick Schuler, a captain with the agency.

The personnel will relieve another local crew of the same size in fighting the so-called Butte Lightning Complex conflagrations near Chico.

The 59,400-acre wildfire, a combination of 41 separate blazes that have destroyed 71 homes, was 90 percent contained as of this morning, according to state officials.

The latest local group to help subdue the nearly 2,100 fires that have plagued the northern reaches of the state over the last month will remain on the lines for at least three weeks, Schuler said.

About 150 San Diego-area state firefighters have joined in the effort to defeat the stubborn lightning-sparked blazes, he said.