A wildfire raced across several areas in Northern California, burning through 40 miles of land area, forcing thousands to evacuate their homes, and injuring four firefighters over the weekend.

Fire department spokesman Daniel Berlant said that the firefighters, who were members of a helicopter crew based in Lake County, have been airlifted to a hospital and are now listed in stable condition, according to USA Today.

The fire started Saturday afternoon in Lake County, which is around 100 miles north of San Francisco, and it easily burned through trees that have been dried by the drought. An unconfirmed number of structures were destroyed, and entire towns, as well as residents along a 35-mile stretch of highway, were evacuated, according to Fox News.

Gov. Jerry Brown declared a state of emergency, helping free up funding and resources in the firefight. About 3,800 firefighters were assigned to fight the fire while the cause is still under investigation, the Associated Press reported.

Meanwhile, the ancient grove of giant Sequoia trees, some of which are 3,000 years old, are threatened by the wildfires. Locals and firefighters are protecting it from the fire by clearing a brush around the Grant Grove, which was named after the General Grant Tree that is 268 feet tall, The Guardian reported.