U.S. Forest Service officials have determined a cause for the Early Fire that blacken more than 1,600 acres last week in the remote Tuolumne River canyon east of Groveland.
Forest Service spokesman Jerry Snyder says their investigation found trees too close to the high voltage power lines sparked the blaze.
The fire had threatened the Hetch Hetchy Early Intact hydro-electric power facility for a time. It was not damaged, although the transmission lines on the Hetch Hetchy power grid were shut off during the fire.
Earlier today, firecrews working mop-up on the fire had called in a helicopter to help douse small fires that were smoldering in the burned area.