For more than four hours, no one heard from Braden Varney. The 10-year veteran of California’s firefighting force had been dispatched to bulldoze a firebreak on a precarious ridge near Marble Point in Mariposa County, an effort to contain the stubborn Ferguson Fire near Yosemite.

It was before dawn on July 14, and the blaze that ignited a day earlier in Sierra National Forest was pushing toward the tiny town of Jerseydale. At first, California Department of Forestry and Fire Protection incident commanders didn’t overthink the lapse in communication. The backcountry was remote and unreachable — maybe Varney didn’t have radio service.

But at 8:47 a.m. a pilot sent to fly over Varney’s last known location spotted his 42,000-pound bulldozer at the bottom of a 220-foot drop. Varney, 36, had become the first fatality in a perilous start to a wildfire season that would kill three more firefighters on active duty as well as four residents by the end of July.

Little was known about Varney’s accident until this week, when Cal Fire completed its Green Sheet, the agency’s report on serious injuries and accidents. While the report does not assign blame, it lists more than a half-dozen safety concerns related to Varney’s death and a list of lessons learned, suggesting that the accident could have been prevented.

Investigations into the deaths of the three other firefighters are ongoing, but together they have called into question how local and state agencies keep firefighters safe as resources are increasingly stretched thin by bigger and more explosive conflagrations.

“Conditions have been really extreme,” said Michele Steinberg, manager of the wildland division for the nonprofit National Fire Protection Association. “They make a more dangerous situation than firefighters might normally face. At night, on steep slopes, in extreme heat and wind, you have conditions where even the most fit individuals can get in trouble.”

Perhaps most striking in Cal Fire’s report was the finding that, over several hundred feet, Varney’s bulldozer slipped partially off the hillside three times — incidents so dangerous they would have been individually red-flagged as signs of potential road failure, the report said. The fourth slip was fatal, sending the bulldozer tumbling to the bottom of a ravine.

The report notes that, in the future, fire supervisors need to maintain communication with crew members, plans should have “tactical value,” and working alone should be “an anomaly, not the rule,” suggesting that officials failed to check in with Varney and didn’t establish a clear and safe mission.

“We are always looking for the common denominators in why there are fatalities on these incidents,” said Cal Fire spokesman Jonathan Cox. “That’s why our department evaluates how and why an incident happened, and if there are changes we need to make as a department.”

Varney was one of the first firefighters from Cal Fire’s Madera-Mariposa-Merced unit to arrive at the Ferguson Fire at 10 p.m. on July 13. At the time, the blaze had only swept across 50 acres, though the report notes that officials knew it had the “potential to become a major fire.”

As of Thursday, nearly 20 days later, it had scorched more than 69,000 acres and was 41 percent contained, or surrounded by natural or carved-out firebreaks. Much of Yosemite National Park remained closed through at least Sunday, due to firefighting operations and smoke.

Because of technical issues, the state report said, Varney couldn’t communicate with the incident commander as he traveled the Hite Cove Trail to the Merced River’s South Fork, where he planned to meet with other bulldozer operators. Instead, he had his swamper — a heavy-equipment supervisor — radio messages for him.

Around 3 a.m., the report said, the swamper left Varney and traveled 2 miles to get a replacement hydraulic line after the bulldozer sustained a small leak. At 4:30 a.m., the swamper called Varney on the radio. He couldn’t find the keys to get the spare part. It was the last time anyone communicated with Varney. Repeated radio calls after that failed.

At 8:47 a.m., Varney’s mangled bulldozer was found at the bottom of a ravine. It had plunged off the mining-era road, toppled several times over and crushed Varney’s chest and neck, according to the report. By 9 a.m., the swamper had reached the ravine on foot, and Varney was confirmed deceased. It would take more than two days for Cal Fire to extricate his body.

“Due to the complexity of the bulldozer rolling down a hill, they have to bring in extrication equipment to remove portions of the bulldozer to get Braden free,” Cal Fire spokesman Jeremy Rahn told The Chronicle at the time. “He was a top-notch dozer operator.”

Varney’s family members, in an email, remembered him for dying “doing what he loved.” He had operated his first snowplow at age 4 and shared a “love of dirt,” or grading, with his father, also a Cal Fire operator, and his 3-year-old son, Noah, who “mastered the mini excavator last year.” Varney also had a 5-year-old daughter, Maleah.

Varney’s death rattled the firefighting community, and more losses soon followed. Three more firefighters died in the Ferguson Fire and the Carr Fire in the Redding area, which became the sixth-most-destructive blaze in California’s history.

Five firefighters have died this year in the state — four on active duty and one during training — and the fire season is just getting started. In 2018, five firefighters died, according to the National Wildfire Coordinating Group. In 2017, seven died. In 2016 and 2015, four died.

“It’s just a real tragedy for the whole fire service because it’s such a family,” said DeeDee Garcia, a spokeswoman for Cal Fire Local 2881, the union that represents the agency’s firefighters. “To have four already this year is rare. It’s something we don’t want.”

In April, an inmate firefighter died during a training hike. The Ferguson Fire killed Varney and Capt. Brian Hughes, 33, of the elite Arrowhead Hotshots, based in Sequoia and Kings Canyon National Parks, who was struck by a falling tree.

The Carr Fire killed Redding Fire Department inspector Jeremy Stoke, 37, whose cause of death has not been released, and Don Smith, 82, a private contractor who perished when his bulldozer was overwhelmed by flames.

Lizzie Johnson is a San Francisco Chronicle staff writer. Email: ljohnson@sfchronicle.com Twitter: @LizzieJohnsonnn