Crew members aboard a runaway maintenance train that barreled down a steep Sierra Nevada slope tried frantically to slam on the emergency brakes before the locomotive derailed, investigators said.

The bodies of two crew members were recovered Friday from the smoldering wreckage of Thursday's derailment, which spilled thousands of gallons of fuel near a thick forest and sparked a large fire. Eight other crew members aboard the train, which was carrying rail equipment, suffered minor injuries.

Survivors told authorities that the men who died had been trying to apply the brakes when the train ran off the tracks in a ravine about 60 miles east of Sacramento.

The emergency brakes slowed the locomotive only slightly before the train's supervisor — in a final, desperate move — threw it into reverse, said Dave Watson, lead investigator for the National Transportation Safety Board.

The train kept rolling and gathering speed, eventually hitting a curve at about 50 mph — twice the recommended speed for that stretch of tracks.

"This was a runaway train," said Watson, who spent Friday interviewing crew members.

"They were pretty much shook up. They were heart-broke," he said in a telephone interview with The Associated Press.

Watson said the stretch of track leading to the crash site is one of the steepest in the country, running straight before it curves where six of the train's 10 cars derailed.

Investigators have come close to ruling out the possibility of faulty tracks at the crash site, he said. The agency is focusing instead on the speed of the train.

Investigators on Sunday planned to comb through two locomotives and two other cars from the accident to find the train's events recorder, similar to an airplane's black box.

Sheriff's Lt. Chal DeCecco, spokesman for the agencies at the scene, said crew members told investigators the train was passing through a tunnel when they noticed something amiss and tried to slow down about three miles before the crash site.

DeCecco said it would take until Monday to positively identify the victims. One body was recovered from a burned-out train car, while the other was underneath the tangle of fire-charred steel.

"It's just a tragedy," said Ken Julian, spokesman for Harsco Track Technologies, the South Carolina-based contractor that employed the victims and all but one of the other crew members. "We're going to do everything we can to support the families and get to the bottom of the cause."

Harsco owns the train, which was transporting a piece of maintenance equipment called a grinding machine under a contract with the Union Pacific Railroad. The lone Union Pacific employee aboard the train was the conductor.

The train's purpose is to smooth worn-down sections of track. It was likened to a "rolling mechanic's shop," with a tanker carrying diesel fuel for the locomotive and the other rail cars carrying equipment and drums filled with an assortment of fuels and fluids.

Crews were clearing the tracks Friday, and the railroad hoped to restore full service on the busy east-west corridor over the weekend. A 600-foot section of track will have to be replaced, Union Pacific spokesman Mark Davis said.

Officials from the U.S. Environmental Protection Agency and California Department of Fish and Game also were on the scene, trying to keep spilled fuel from running into a tributary of the north fork of the American River.