Two fires in the Lassen National Forest have burned more than 66,000 acres.
The lightning-caused Bald Fire is 20 percent contained Monday and is burning south of Fall River Mills in Lassen County.
Fire officials say the Bald Fire has burned less actively, spreading primarily to the south and it is 20 percent contained.
Just to the west of that fire is the 25,900 acre Eiler Fire, which is 4 miles southeast of Burney.
The fire is burning in timber and brush and is spreading more rapidly.
Officials are concerned about thunderstorms and the increasing chance of more lightning-caused fires in areas that are tinder-dry after three years of drought.
More than 3,000 firefighters are working to control both wildfires.
The two Lassen County fires are among 10 active fires burning in California. The other wildfires are in Mariposa, Madera, Mendocino, Modoc, Shasta and Siskiyou counties.
BALD FIRE: http://inciweb.nwcg.gov/incident/4022/
EILER FIRE: http://inciweb.nwcg.gov/incident/4037/