It all starts with a line in the dirt.

When a wildfire sparks anywhere in the back country, it’s the fireline that is the first defense. Before the air tankers, the helicopters, and hundreds of fire engines, it’s a small team with shovels and hand tools scratches a fireline down to mineral soil to surround the fire and stop its spread.

NBC News was given unprecedented access to one of the most dramatic of firelines — the front lines of the 100,000-acre Happy Camp Complex fire in northern California. To date, the U.S. Forest Service has spent more than 70 million dollars to fight this fire, started by lightning in mid-August. More than 150 square miles of heavy timber has burned, covering incredibly steep mountains in the Klamath National Forest. Homes and small communities are threatened, but none have been lost so far.

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As the fire grows, the line moves with the fire, flanking the head of the fire all the way. Working the line 10 miles from the fire’s origin, Nolan Reynolds, a USFS engine crewmember, says “the anchor of the fire is way back there”, pointing back into the thick steep forest. “We have to make sure nothing burns over this line, because if it does all of our work is for nothing. The guys further up the line … we have to watch their back to make sure there’s no fire behind them.”

At the height, 2,800 people are working on this fire around the clock. Firefighters from as far away as North Carolina and Virginia, who are making their summer swing through the west, come to help. This will probably be the last big fire of the season for most of these teams. Northern California is suffering from incredible drought, making fire bosses worry about the explosive potential in the woods.

“When you go to a lumberyard and you get a 2x4, it’s like 12% (fuel moisture). Well, the fuels around here are running 5-7%, so all the trees, all of the brush, everything is fuel for the fire”, says Jeanne Pincha-Tulley, the Incident Commander. She’s been fighting fires in the woods for more than 30 years and says they can sneak up on you in a heartbeat. “I think a lot of people think we go in and just choose the next ridge. No! We have multiple plans because the fire moves so fast. You can go from your direct plan to your fifth contingency in 15-20 minutes on some fires.”

For the firefighters, each day begins early with a 6 a.m. briefing, then out to the line for at least a 12-hour shift, then back to camp to sleep in the dirt in a sleeping bag.

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Firefighters stand on a 60-degree slope at the Happy Camp Complex, as they dig fireline, clear brush that might spread a fire, “mop up”- work through a burned area to make sure all hotspots are completely cool so they don’t rekindle.

It’s incredibly hot and dirty work. Crews joke that it should be called “coal mining above ground”. Fire crews will spend the summer together, travelling from fire to fire. Michael Lamez, who runs a chainsaw for a crew out of northern California, says the grind of the job is taxing. “I haven’t had any contact with my family for like 3, 4 days now, so I’m sure they’re probably pretty worried, wanting to know what’s going on. On the other hand, that’s what we gotta deal with, there’s no phone out here.” His squad boss, Mathew Beccaria, says the brotherhood in the woods is a strong bond. “My family’s out here as much as my family at home, so that’s the way I treat it. These are my kids and I gotta watch out for them.” The pressure to keep everyone safe a constant worry.