B.L.M. officials say the Brush Creek Fire is now at 150-acres. Structures to the west are now within a half mile of the wildfire. Oil and gas facilities are a few miles northeast.
Investigators have determined the fire was sparked by lightning.
It's burning near Douglas Pass on B.L.M. public land, 17-miles east of the Utah border. It's located in heavy timber on Pike Ridge in an area that's difficult for firefighters to access.
According to Lynn Barclay with the B.L.M., fire activity increased Wednesday night and the blaze backed into the Brush Creek drainage.
Air tankers continue to drop retardant on the west flank to protect the structures and give firefighters an opportunity to work in that area.
Barclay said dozens are en route to build a fire-line around the structures as well. Engines will continue to guard the residences in the area.
The B.L.M.'s highest area of concern is the west flank; other control issues are dry fuels, poor access and tough terrain, said Barclay.
A local Type-3 Incident Management Team is handling the wildfire.
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