Austen Thibault, The Union Democrat

A wildfire near Donnell Reservoir had spread to 275 acres as of 7:30 a.m., according to the latest update from the Stanislaus National Forest.

The Power Fire, named for being so close to the Donnell powerhouse, grew about 100 times in size since Monday morning.

The blaze was first called in about 5:30 a.m. Monday on Hell's Half Acre Road, on the east side of Donnell Reservoir, according to 911 dispatch logs.

The caller estimated it to be about 3 to 4 acres at the time, and the initial reports from Forest Service firefighters estimated it as even smaller, 1 to 2 acres, according tonational forest spokeswoman Veronica Garcia.

But the fire swept up a canyon and grew to an estimated 100 acres as of 10:30 a.m. Monday, said Garcia.

The Forest Service warned that the blaze threatens the Donnell Curtis Transmission lines, which firefighters are working to protect.

It also closed Highway 108 for a time.

The fire was reportedly "right near" the Donnell powerhouse in its early stages, said Garcia.

But as it grew, the fire moved away from the powerhouse, according to Ron Berry, operation supervisor of Tri-Dam Project, which operates the Donnell Reservoir powerhouse.

Berry said one operator is working at the powerhouse and one other employee and his wife also live in a home next to the powerhouse.

No evacuations have been called, but notifications have been given to nearby residents and campers, according to the Forest Service.

Keeping the station running may actually help the firefighting cause, as the penstock, the large above-ground pipe water comes in from, will stay cold and full of water, Berry said. The pipe carries up to 5,280 gallons a second into the powerhouse, he said.

It may defend itself in this way, Berry said, which is important because losing the penstock would completely halt the powerhouse and cost millions of dollars in damages, repairs and lost revenue.

Also, the employee at the powerhouse has been assisting firefighters with water supplies as he closely monitors the area for safety.

A cause and point of origin are still under investigation.