Without pointing to a specific cause for last week's fire at Maidu Park in Roseville, investigators made clear Monday they believe the blaze was intentional.
"It is being classified as an arson fire," said Fire Marshal Jason Rizzi. "There is no other explanation for that fire to start at that time."
The 2:25 p.m. Friday blaze in the park's nature preserve was fueled by high winds and dry conditions. It burned five structures, causing $1 million in damage.
Investigators looked into other potential causes for the 30-acre fire such as mechanical, weather or electrical but no other origin was deemed plausible, Rizzi said.
Initial media reports noted a group of young people leaving the area of the fire, but Rizzi said Monday he did not have information to corroborate those reports.
Given the proximity of the homes to the recreation area of trees and grassland, the department quickly asked for help from surrounding fire agencies.
Sacramento Metro, Rocklin and South Placer, and Folsom fire departments and the state Department of Forestry and Fire Protection were among the agencies to dispatch units. Some 180 firefighters were involved, Rizzi said.
Embers carried the fire onto four homes and a gazebo, all with wood-shingle roofs. Rizzi noted that homes with more fire-resistant roofs did not catch fire.
He encouraged homeowners with wood-shingle roofs to re-roof with a safer material such as composite, tile or metal.
Investigators from the Roseville Police and Fire departments are asking anyone with information to contact the Roseville Police Department at (916) 774-5070.
Call The Bee's Ed Fletcher, (916) 321-1269. Follow him on Twitter @newsfletch.