By CBSLA Staff

NEAR VALYERMO (CBSLA) — Fire crews Tuesday continued to battle a brush fire which broke out in the Angeles National Forest.

April 5, 2021. (CBSLA)

The Spring Fire broke out south of Valyermo shortly after 4:15 p.m. Monday in the area of Big Pines Highway and Big Rock Creek Road.

READ MORE: Pittsburgh Man Claims Rams Star Aaron Donald Assaulted Him

According to Angeles National Forest officials, the fire was burning in an area of medium-to-heavy fuels and was backed by gusty winds of 20 to 30 miles per hour. It quickly grew from 20 to more than 50 acres.

U.S. Forest Service and the Los Angeles County Fire Department crews responded.

Just before 7 p.m., officials said strong air attacks appeared to be holding the fire at approximately 60 acres and that some structures, including a fire training camp, were threatened by the flames.

READ MORE: Hawaii Lifts Quarantine Requirement For Travelers Flying Out Of Ontario International Airport

It was unclear Tuesday morning if crews had established any containment lines around the blaze.

The cause of the fire was still under investigation.