The fire was 1 1-2 miles from the observatory by Friday night, prompting a precautionary evacuation although authorities said few people actually stay at the eastern Arizona facility in the Pinaleno Mountains.
Fire spokeswoman Jennifer Plyler said the observatory recently implemented a fire risk reduction project with a 200-foot defensible space around the facility along with a sprinkler system and water storage tank.
The Gibson fire "has the potential to test the work that they have been doing" at the observatory, Plyler said.
The blaze began June 22 and had remained small in steep terrain until Friday "when it just took off," Plyler said.
The fire was six miles east of the lightning-caused Nuttall fire, which began June 26 and had charred 2,500 acres by Friday night. It remained on the northwest flank of Mount Graham and was not threatening any structures.
However, some firefighters were briefly pulled off the Nuttall fire Friday and about 10 firefighters had to deploy emergency shelters.
The shelters, which are like tents that can be shaken open in an emergency, are used by firefighters trapped by oncoming flames.
However, officials did not know why the firefighters had to use the shelters about 1:45 p.m. as fire activity increased because they were still working on the mountain Friday night, Plyler.
"Everyone is OK. There were no injuries," Plyler said.
However, the wildfire was back to 5 percent containment by Friday night after being at 10 percent contained earlier in the day, Plyler said.
About 580 firefighters worked to strengthen lines and conduct burnout operations along the eastern perimeter of the fire Friday.
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WILLOW FIRE
PAYSON, Ariz. (AP) - A lightning-caused wildfire burning near Payson has grown to 65,000 acres but remained four miles southwest of the community.
The Willow fire was 8 percent contained Friday night, up from 5 percent on Thursday.
Carrie Templin, a spokeswoman for the crew fighting the blaze, said recent burnout operations had pushed back the perimeter of the fire to six miles from Payson on Thursday but flames had spread northeast toward the community of 14,000.
Firefighters were working to strengthen lines and conduct burnout operations on the northeast portion of the fire, the edge closest to Payson.
Crews planned to complete a fire line overnight Friday on the southeast side of the blaze.
The fire had grown by about 10,000 acres from Thursday to Friday as it spread mostly northwest - away from the three nearby communities.
Seventeen buildings, including homes, barns and sheds, were considered threatened by the fire, but there were no evacuations.
Authorities said 951 firefighters were working to stop the blaze, which has been burning cypress trees, chaparral and brush since June 24.
Authorities said the cost of fighting the fire had reached $3.2 million by Friday.
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UPSHAW FIRE
SAN CARLOS, Ariz. (AP) - A wildfire has charred about 2,000 acres of rough mountainous terrain here but wasn't threatening any structures.
Fire officials said the fire was 90 percent contained by Friday night with full containment now expected Saturday night.
About 270 firefighters mopped up and looked for hot spots around the Upshaw fire, which was burning on the San Carlos Indian Reservation, said Arnall Swift, supervisor dispatcher for San Carlos Fire Management.
The fire was started by lightning on Monday.
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TOUCAN FIRE
KEARNY, Ariz. (AP) - A 50-acre fire south of Kearny briefly forced the residents of about 40 trailers and a few houses to flee Friday. Everyone was back home by nightfall, authorities said.
Bureau of Land Management spokeswoman Nancy Guerrero said firefighters had attacked the Toucan fire when it was first reported early in the afternoon. It had scarcely grown by Friday night.
"As long as they hit it really hard initially, we're able to just take care of it quickly," Guerrero said.
No containment figures was immediately available and Guerrero said the cause of the fire was unclear.
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