Touring the area over the weekend alongside the state’s outgoing and incoming governors, Jerry Brown and Gavin Newsom, the US president twice used the wrong name for the town where most of the 77 people known to have died so far have come from.
“You’re watching from New York or you’re watching from Washington, DC, and you don’t really see the gravity of it,” he said.
“I mean, as big as they look on the tube, you don’t really see what’s going on until you come here. And what we saw at Pleasure, what a name right now, but what we just saw, we just left Pleasure...”
He was then interrupted by the crowd, who corrected him.
“Or Paradise,” Mr Trump added. “And what we just saw at Paradise is just, is just not acceptable.”
Mr Trump also insisted he had not changed his mind on climate change after visiting the town in northern California.
“I have a strong opinion,” he said. “I want great climate, we are going to have that and we are going to have forests that are very safe.”
He appeared to blame forest management for the fires.
“We’ve got to take care of the floors, you know the floors of the forest, very important,” he said. “You look at other countries where they do it differently and it’s a whole different story. I was with the president of Finland and he said … we’re a forest nation, he called it a forest nation, and they spend a lot of time on raking and cleaning and doing things. They don’t have any problem, and what it is, it’s a very small problem.”
Finland's leader Sauli Niinisto later told the Ilta-Sanomat newspaper that he had spoken briefly with Mr Trump about forest management on 11 November, when they both were in Paris for Armistice Day events.
He said their conversation had focused on the California wildfires and the surveillance system Finland uses to monitor forests for fires.
He said he remembered telling Mr Trump that “we take care of our forests”, but could not recall raking coming up.
In California, rain is forecast for the area this week, potentially helping to douse the flames which have been raging since 8 November.
The death toll far surpasses the previous fatality record from a single California wildfire, 29 in the Griffith Park fire on 1933 in Los Angeles and already ranks among the deadliest US wildfires since the turn of the last century.
It was also the most destructive in California’s history, having destroyed more than 13,600 homes and other structures.
Mr Trump also visited southern California, where firefighters are making progress against another wildfire which tore through communities from Thousand Oaks to Malibu, killing three people.
Additional reporting by agencies