Firefighters lined roads to keep flames from reaching homes as helicopters dropped water on a growing wildfire Wednesday in Northern California that has forced at least 26,000 people to evacuate, as the state sweltered under extreme heat.

The Thompson fire broke out before noon Tuesday about 70 miles north of Sacramento, near the city of Oroville in Butte County. It sent up a huge plume of smoke that could be seen from space as it grew to more than 5.5 square miles . There was no containment.

But Oroville Mayor David Pittman said by Wednesday afternoon there had been a “significant drop in the fire activity,” and he was hopeful that some residents could soon be allowed to return home. The fire’s progress was stopped along the southern edge and firefighters working in steep terrain were trying to build containment lines on the northern side.

“On that north side they have some real struggles in terms of the topography,” Pittman said.

More than a dozen other blazes, most of them small, were active in across the state, according to the California Department of Forestry and Fire Protection, or Cal Fire. A new fire Wednesday afternoon prompted a small number of evacuations in heavily populated Simi Valley, about 40 miles northwest of downtown Los Angeles.

The state's largest blaze, the Basin Fire, covered nearly 22 square miles of the Sierra National Forest in eastern Fresno County and was 26% contained.

In Oroville, a state of emergency was declared Tuesday night and evacuation centers were set up. The evacuation zone expanded Wednesday into foothills and rural areas beyond the city that’s home to about 20,000 people. With July Fourth in mind, authorities also warned that fireworks are banned in many places, including most of Butte County.

There was no immediate official report on property losses. An Associated Press photographer saw fire burn three adjacent suburban-style homes in Oroville.

The fire ignited sprigs of grass poking from the concrete edges of Lake Oroville as gusty winds whipped up American flags lining a bend of the state’s second largest reservoir and the nation’s tallest dam.

Residents stood on hillsides in the night, watching the orange glow, as aircraft made water drops to keep the fire from spreading. A crew of more than a dozen firefighters saved one home as goats and other farm animals ran to find safety.

The fire's cause is being investigated. Red flag warnings for critical fire weather conditions, including gusty northerly winds and low humidity levels, were in effect when it erupted.

The warnings were expected to remain in effect until 8 p.m. Wednesday, said Garrett Sjolund, the Butte County unit chief for Cal Fire.

“The conditions out there that are in our county this summer are much different than we’ve experienced the last two summers,” Sjolund said in an online briefing. “The fuels are very dense, brush is dry. And as you can see, any wind will, move a fire out very quickly.”

The conditions led Pacific Gas & Electric to implement targeted public safety power shutoffs in parts of some Northern California counties to prevent fires from being ignited by downed or damaged wires.

More high temperatures above 100 degrees were forecast Wednesday, the National Weather Service said. Hot conditions were expected to continue into next week.

Authorities warned of full legal consequences for any illegal use of fireworks during the Fourth of July holiday.

“Don’t be an idiot, cause a fire and create more problems for us,” said Butte County Sheriff Kory L. Honea. ”No one in the community is going to want that. And we certainly don’t want this.”

The governor’s office announced late Tuesday that federal funding had been approved to help with firefighting efforts. Gov. Gavin Newsom this week activated the State Operations Center to coordinate California’s response, dispatch mutual aid and support communities as they respond to threats of wildfire and excessive heat.

In Southern California, Joshua Tree National Park officials closed Covington Flats, an area with most of the park’s important Joshua tree populations, on Wednesday because of extreme fire risk after spring rains led to abundant grass that has now dried. A June 2023 fire burned 1.6 square miles of Joshua trees and desert tortoise habitat.

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