The fire was human caused. Most likely in a shooting quarry. What was of interest to me was that they used the abandoned road that starts the Sunday Lake trail as the fire line. These two photos with Nim closer to the trees is actually closer to the site of the fire at the quarry. The quarry is just before you go over the bridge towards forest service road 57.
After we explored the initial fire site, went drove back to the Sunday Lake trail head and really started exploring. I was impressed at how they managed to get equipment through the swamp and wetlands that start the trail. It was obvious they had used vehicles with tracks as opposed to tires (at least as well as I could see). I think this was probably the best solution for getting through the notorious deep swamp.
Even in the heat of summer, the tracks would have done the least damage and allowed the sensitive area to rebound.
They are regrettably very hard to capture in a photo. But that didn't stop me from trying. I have never had this much visual access to them.