More than a week after wildfires began blazing in Oregon, Washington and California, false and exaggerated claims about the fires’ origins are still spreading like, well, wildfire.

The latest, most viral rumor involves Domingo Lopez Jr., a 45-year-old man who was arrested in Portland, Ore., on Sunday, and again on Monday, on suspicion of starting a series of small fires. During one of these arrests, the police photographed a bottle with a wick attached, a Molotov cocktail they said Mr. Lopez had used to start one of the fires.

Local news reports noted at the time that all of the fires Mr. Lopez was suspected of setting were quickly extinguished, and that no people or buildings were harmed. They also noted that Mr. Lopez was taken for a mental health examination after his arrests.

Still, right-wing websites and conservative media influencers ran with the story about Mr. Lopez and his Molotov cocktail — often omitting from their headlines the fact that none of those fires caused any damage, or were related to the larger blazes that have driven thousands of people from their homes.

“Man Arrested for Starting Oregon Fire Gets Released Without Bail, Sets 6 More Fires,” read one headline, by the pro-police news outlet Blue Lives Matter. The article was shared roughly 40,000 times on Facebook. Breitbart, the far-right news site, also shared the story, getting more than 27,000 Facebook shares on a post whose headline also left out the details of the fires.

Dinesh D’Souza, the right-wing filmmaker, posted a meme with Mr. Lopez’s mug shot, in which he cast doubt on the scientific claims that the wildfires were caused by global warming.

As The New York Times’s Michael Grynbaum and Tiffany Hsu reported on Tuesday, many conservative media figures, including Rush Limbaugh and Tucker Carlson, have aligned themselves with President Trump in an effort “to generate a deep skepticism of the notion that climate change is a factor in the fires devastating the West Coast.” Some of these figures have been pushing the unfounded narrative that arsonists and antifa sympathizers are responsible for setting the wildfires.

Law enforcement agencies, including the Federal Bureau of Investigation, have dispelled that rumor, and scientists say that climate change is the primary factor behind the blazes.