Kevin Winter/Courthouse News

OAK, Calif. (CN) — A fire near Yosemite National Park — the second in or near the famed park already this season — has destroyed several structures and threatens thousands more as thousands flee and unhealthy air blankets much of the central Sierra.

The Oak Fire began July 22 near the small community of Oak and in a matter of hours grew to over 10,000 acres. As of Monday morning the fire blackened 16,791 acres and is 10% contained. The fire has been moving north, south and east from its origin. The cause of the fire is under investigation.

Crews from Cal Fire have been worked on building containment lines and protecting structures as the fire has swept through the dry and drought-stricken trees and other plant life throughout the area.

The fire is currently just burning northeast of the town of Mariposa and has closed Highway 140 between Midpines and El Portal at the entrance to Yosemite National Park — though the park remains open to visitors via highways 120 and 41.

Cal Fire noted in its Monday morning report that the fire remained active throughout the evening as it churns through a combination of dead and down fuels that are dry because of the drought. Several homes have been destroyed.

On Sunday crews stopped the fire’s southern movement and will continue to mop up hot spots and monitor the situation.

The eastern flank of the fire presents more challenges for firefighters due to steep terrain, heavy fuels and dry conditions. Cal Fire is working on stopping the fire at Footman Ridge on the eastern flank. Meanwhile, crews will continue protecting structures in the community of Mariposa Groves and find a way to stop the fire near Bear Clover Road before it moves over the mountains and into Yosemite.

As in the first few hours of the fire, crews have noticed occasional crowning — when the canopy of the forest is on fire — which drives the fire to grow by thousands of acres a day and threaten structures.

Given containment efforts from Sunday into Monday, Cal Fire hopes for full containment by this weekend.

Crews including 2,500 personnel, 46 water tenders, 66 dozers and 17 helicopters are working to contain the fire and protect structures. No injuries or fatalities have been reported.