Authorities arrested two men in their early 20s this week after a bystander reported seeing them attempting to set a fire off the side of a road near the Morris Reservoir Dam in Angeles National Forest, officials said Thursday.

The bystander called 911 after spotting the two men’s suspicious activity around 3 a.m. on Tuesday. They allegedly sparked a hillside to the west of Highway 39 about six miles north of Azusa, the Los Angeles County Sheriff’s Department said in a news release.

The caller described the suspects’ appearance and gave the license plate number on the white truck he saw them flee in, authorities said.

Deputies and firefighters responded to the location and found a quarter-acre blaze. California Highway Patrol responded to shut down the road, and fire crews were able to promptly put out the flames with water-dropping helicopters, sheriff’s officials said.

Meanwhile, police in Azusa located the suspects near the corner of Sierra Madre Avenue and Vosburgh Drive and detained them. Inmate records show they were taken into custody around 4 a.m.

Both men were subsequently booked on suspicion of arson, officials said.

Christopher Ortega, 20, was being held on $285,000 bail, while 21-year-old Santino Gnaulati was booked on $75,000 bond, the Sheriff’s Department said.

The U.S. Forest Service is now investigating the incident. No further details were available.