Authorities arrested a man Monday for allegedly sparking one of several uncontained Washington state wildfires that have so far scorched thousands of acres and forced tens of thousands of people to evacuate their homes.

The Spokane County Sheriff's Office said authorities arrested Aaron Farinacci, a 37-year-old Spokane resident, on a first-degree arson charge related to one of three major fires burning in the eastern Washington area. He is being held on a $1 million bond and was previously convicted of manslaughter in Arizona, the sheriff's office said.

Three uncontained wildfires in eastern Washington have burned through more than 8,000 acres and destroyed hundreds of structures since the start of the month. Officials in Spokane County said Monday that authorities estimate at least 600 structures have been "impacted throughout the fire area."

Spokane Mayor Lisa Brown called the fires "the worst natural disaster our region has faced." The state's Department of Natural Resources described this wildfire season as "already the most challenging, devastating fire season our state has experienced in years." Thirteen large fires are burning across the northwestern state, according to state data, with the number of acres burned so far this year amounting to the highest since 2021.

Authorities narrowed in on Farinacci following a tip from a citizen, Spokane County Sheriff John Nowels said during a press conference. A resident driving in the area where the fire started spotted a man kneeling in grass before standing up and "looking very nervous," Nowels said. Authorities believe the suspect used matches or a lighter to spark the blaze, which Nowels said they believe started within 10 square meters of where the suspect was initially spotted.

It wasn't immediately clear whether Farinacci had legal representation.

Firefighters made some progress containing the rapidly spreading fires over the weekend due to cooler temperatures, Spokane County officials said. Temperatures are forecast to rise, and wind later this week could heighten conditions for fire to spread more easily, according to the National Weather Service in Spokane.

Washington Gov. Bob Ferguson declared a statewide wildfire emergency Saturday as the state contends with ongoing drought. The Democratic governor said he requested federal assistance to help contain the wildfires.