Electricity to 18,000 Sierra Pacific Power Co. users was knocked out just before lunchtime on Thursday.
Gary Aldax, spokesman for the power company, said breakers tripped on two transmission lines serving Dayton, Fernley, Fallon, Mark Twain and Yerington at 11 a.m.
"About half the customers were back on by noon," he said. "Everyone else was back by 1 p.m.
The source of the power outage is still being investigated.
"We're still working on finding the cause," he said. "The safety equipment on a couple of transmission lines tripped off."
Temperatures reached triple digits in Fallon and were in the mid to upper 90s elsewhere.
None of Lyon County's emergency services were affected by the outage, according to the Lyon County Sheriff's Department.
Meanwhile, construction began on a new power line to increase service to Fernley, Fallon and Storey County.
Sierra Pacific Power Co.'s 25-mile line will run east of the Tracy substation, west of Fernley, to Eagle substation, northeast of Fernley and north of Interstate 80.
Operation is scheduled for October, said Aldax. The project not related to a 40-mile, 120-kilovolt line slated to run through Douglas and Lyon counties.
Aldax said Sierra Pacific obtained an easement from the city of Fernley in a May 20 meeting and has begun installation. The 120-kilovolt line will run parallel to an existing line for only part of the way.
"The new line will provide system reliability and capacity to the Fernley, Fallon and Storey County electric grids," Aldax said.
The line will also provide future service capability to the Tahoe Reno Industrial Park, off I-80, just west of the Tracy substation.