A California man has pleaded not guilty to starting a fire that authorities said ballooned into the rapidly spreading Line fire that has scorched at least 39,000 acres (15,783 hectares) and forced the evacuations of thousands of homes.

Online court records show that Justin Wayne Halstenberg, 34, entered the plea from jail in a video arraignment Tuesday in the San Bernardino city of Rancho Cucamonga. He was denied bail and appointed an attorney, the records show.

Halstenberg’s next court appearance will be Monday. An email message was sent to the attorney listed on his behalf.

Halstenberg is charged with 11 arson-related crimes, the records show.

Prosecutors in the San Bernardino county district attorney’s office allege that Halstenberg, a delivery driver from the town of Norco, tried to start a fire in at least two other locations before succeeding. The first, on Bacon Lane in Highland, California, was reported and extinguished by firefighters. “The second was stomped out by a good Samaritan,” the district attorney’s office said.

“Undeterred, he ignited a third fire which is what we now know as the Line fire,” prosecutors said in the statement.

Halstenberg’s mother, Connie Halstenberg, told the Los Angeles Times on Saturday that there were things that her son has done that she does not approve of but that “he is not an arsonist”.

Prosecutors said additional charges may be filed for any further structure damage or injuries as the fire continues.

Authorities have said Halstenberg’s vehicle has been tied to areas where the fires were started on 5 September.

The Line fire has threatened more than 65,000 homes and injured four firefighters. It is one of three wildfires that exploded across southern California this month following a triple-digit heatwave.

The full extent of the damage caused by the blaze remains unclear, but Jason Anderson, the San Bernardino county district attorney, said at least one home had been destroyed.

Firefighters gained ground on the Line fire over the weekend as well as increasing containment on two other southern California wildfires as authorities in northern Nevada lifted the last of evacuation orders for all homes Sunday.

The Line fire was 49% contained as of Tuesday afternoon thanks to below-average temperatures and moderate relative humidity overnight.

The largest southern California blaze, the Bridge fire, which exploded dramatically through the Angeles national forest east of Los Angeles at the start of the week, has burned more than 54,000 acres. It also has torched at least 66 structures and injured at least four people, and is just 25% contained.

The Airport fire in Orange and Riverside counties has kept steady at 23,000 acres. It has destroyed at least 160 structures and injured 14 people.

“We’re being helped by the weather and that weather will continue for a couple of days so we’re making good progress,” said Albert Ward, the Orange county fire authority operations section chief.

Despite favorable weather, there is still fire risk above 4,000 feet (1,200 metres) in elevation, which remains dry. Smoldering vegetation up high can roll downhill and ignite unburned vegetation, the fire authority said.