Resources were sent to the Low Mountain fire, which was burning about 1,000 acres Wednesday. The fire, centered about 15 miles south of St. George in Arizona, was started Tuesday by a lightning strike.
About 80 firefighters, four single engine tankers and two helicopters were fighting the new fire, said Bureau of Land Management spokesman David Boyd.
Some cell and radio towers were threatened but the air support had been protecting them well, Boyd said.
About 320 firefighters, three helicopters and 10 engines remained on the Square Complex fire 14 miles north of St. George.
No homes were threatened by any of the fires and no major injures had been reported.
The Square Fire Complex was 40 percent contained on Wednesday. It hasn't burned any new ground since Sunday, and fire officials estimated it could be 80 percent contained by early Thursday and fully contained by Sunday.
The Square Fires were sparked by lightning Friday. So far, 17,979 acres have been burned.