120 fire fighters are battling to contain the blaze, which has destroyed 20 structures, KEYT reported.
Elsewhere in California, a massive blaze north-west of Sacramento that began June 30 had destroyed 10 homes and other buildings but was 42 percent contained, officials said.
Santa Barbara County Fire says crews expect to have full containment of the Holiday Fire in Goleta by July 11. Officials believe human activity sparked the blaze, but an exact cause hasn't been determined.
The fire is located about a mile northwest of Basalt and was started Tuesday by two people firing tracers at a firing range near Christine Lake.Three houses have been destroyed.
The governor has declared states of emergency in Siskiyou, San Diego and Santa Barbara counties this week due to fires.
The flames forced more than 2,000 people to flee their homes, and left thousands more without power, prompting the emergency declaration which frees additional funds for the firefighting effort. Neither of those fires are contained yet.
The Klamathon Fire more than doubled in size Friday night, roaring to 21,800 acres on the OR and California border.
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What's happened: The fire has more than doubled in size since Friday evening, and crossed the border into OR last night, Cal Fire said.
The fire is one of several that have ignited in southern California Friday, where temperatures topped 100 degrees.
In San Diego County, several fires erupted, including one that burned at least five homes and perhaps many more in Alpine, in foothills not far from San Diego.
County fire Capt. Dave Zaniboni tells KNX-AM radio that he saw homes burning Friday night in a residential area.
Cal Fire-Butte County also tweeted that more than 100 of its members are working "out of unit" helping fight fires throughout Northern California.
"We will not be hard-pressed, we are ready should something happen in the county", he said.
The County Fire in Napa and Yolo counties increased in size to 88,375 acres Friday and was 37 percent contained, Cal Fire said.
The Klamathon Fire broke out on Thursday and, within hours, spread from an initial 1,000 acres to 8,000 acres (3,237 hectares), the California Department of Forestry and Fire Protection said in an advisory.