"He came forward on his own accord," Reno Fire Chief Michael Hernandez said. "He has given statements to our investigators as well as law enforcement officers. He is extremely remorseful."
Fueled by 82 mph wind gusts, the blaze burned nearly 3,200 acres and forced the evacuation of up to 10,000 people Thursday.
A break in the weather and calmer winds allowed firefighters to get the upper hand on the blaze Friday.
Hernandez estimated it to be 65 percent contained Friday night. He said 300 firefighters would remain on the scene through the night checking for hot spots along with another 125 support people, including law enforcement officers and the Nevada National Guard.
The next challenge may be the forecast for rain and snow in the mountains on Saturday, which officials fear could cause flooding in burned areas.
The Highway Patrol said Friday night that all of U.S. Highway 395 between Reno and Carson City had reopened.
Washoe County Sheriff Mike Haley said a formal case file will be forwarded to the district attorney next week for consideration of charges.
"The DA will have to give this case a lot of deliberation," Haley said.
"The fact he came forward and admitted it plays a role. But so does the massive damage and loss of life," he said. "It's a balancing act."
In addition to the potential for facing jail time on arson charges, the man could also be ordered to pay the cost of fighting the fire, which already totals $690,000.
Washoe County Manager Katy Simon said she expects the final bill to run into the millions of dollars.
Gov. Sandoval toured the fire damaged area Friday, describing it as "horrendous, devastating."
"There is nothing left in some of those places except for the chimneys and fireplaces," he said.
The blaze started shortly after noon Thursday and, fueled by the wind, mushroomed to more than 6 square miles before firefighters stopped its surge toward Reno.
The strong, erratic winds caused major challenges for crews evacuating residents, Sierra Front spokesman Mark Regan said. "In a matter of seconds, the wind would shift," he said.
Haley confirmed that the body of June Hargis, 93, was found in the fire's aftermath, but her cause of death has not been established, so it's not known if it was fire related.
Jeannie Watts, the woman's 70-year-old daughter, told KRNV-TV that Hargis' grandson telephoned her to tell her to evacuate but she didn't get out in time.
About 2,000 people remained subject to evacuation, and about 100 households still were without power.
Marred in Reno's driest winter in more than 120 years, residents had welcomed the forecast that a storm was due to blow across the Sierra Nevada this week.
Instead, thousands found themselves fleeing their homes Thursday afternoon.
Connie Cryer went to the fire response command post Friday with her 12-year-old granddaughter, Maddie Miramon, to find out if her house had survived the flames.
"We had to know so we could get some sleep," Cryer said, adding her house was spared but a neighbor's wasn't. She had seen wildfires before, but nothing on this scale.
"There was fire in front of me, fire beside me, fire behind me. It was everywhere," she said. "I don't know how more didn't burn up. It was terrible, all the wind and the smoke."
Fire officials said Thursday's fire was "almost a carbon copy" of a blaze that destroyed 30 homes in Reno during similar summer-like conditions in mid-November.
State Forester Pete Anderson said he has not seen such hazardous fire conditions in winter in his 43 years in Nevada. Reno had no precipitation in December. The last time that happened was 1883.
An inch of snow Monday ended the longest recorded dry spell in Reno history, a 56-day stretch that prompted Anderson to issue an unusual warning about wildfire threats.
"We're usually pretty much done with the fire season by the first of November, but this year it's been nonstop," Anderson said.
Kit Bailey, U.S. Forest Service fire chief at nearby Lake Tahoe, said conditions are so dry that even a forecast calling for rain and snow might not take the Reno-Tahoe area out of fire danger.
"The scary thing is a few days of drying after this storm cycle and we could be back into fire season again," he said.
Associated Press writers Michelle Rindels in Las Vegas and Sandra Chereb in Carson City, Nev., contributed to this report.