The Federal Aviation Administration confirmed Monday that two people died while fighting fires in California’s Yosemite National Park after their helicopter crashed in Mariposa County. 

The two died Sunday afternoon while battling the Dome fire, which started last Tuesday near Wawona Dome inside Yosemite National Park, activating over 500 crisis responders. The FAA said one passenger and one crew member on board were killed after the helicopter “crashed under unknown circumstances while on water bucket drops.”