IT WAS OCTOBER 1998 when Avalon showed up at the cabin I shared with my partner, Stan, outside Eugene and asked if we wanted to take part in a really big action. It would be my first arson, and it would be Stan's first action of any kind. We said yes. We went on a walk in the meadow, because we never discussed anything indoors. A few days later, we followed Avalon east in my truck. We didn't know where we were going until we got to Colorado. He told us the target was the Vail ski area.

I had read about Vail's plans to expand into an 885-acre wilderness where, 15 years prior, Colorado's last wild lynx had been spotted. Vail Resorts seemed like the worst of the worst: not only destroying critical habitat but also destroying local businesses and communities. All for corporate profit earned by building second homes. There had been a large public-outreach campaign, administrative appeals, and lawsuits, but it was still going to happen. If any company deserved to be targeted, Vail did.

In the predawn hours of October 19, with everyone else but me gone back to Oregon and with no timers, Avalon set all the fires himself, by hand. He had to travel on foot, running from building to building on the mile-and-a-half-long ridge. As he lit the last ones, the flames from the first ones were lighting up the sky. There were some scary moments. A hunter was sleeping in a heated restroom in one of the buildings. Avalon opened the door, saw him there, and left it alone.

Down below, I had no way to be sure he'd be back on time. When I was returning from my campsite to pick him up, I heard over the scanner that the police and fire departments were looking for a blue pickup, which was exactly what I was driving. There was nothing to do but keep going. I had to meet Avalon down in town, at a popular trailhead.

I got there right on time. It was morning, it was light out, and day hikers were showing up. I stayed in my truck and shuffled through my things, pretending to be getting ready for a hike. Up on the trail, Avalon had exchanged his black clothing for the hiker's garb that he'd carried in a backpack, and whenever he heard voices coming, he stepped into the woods and hid.

I waited ten minutes, then 20. After a half-hour, as I was wondering if I should leave, Avalon appeared. He just walked up to the truck and got inside. He said two things: He was injured. And the action was successful. It wasn't the time to get details. I just drove.

The first thing we did was go to a library in Denver, and I looked up his injury: a strained Achilles tendon—he'd done too much running. It required ice, not surgery. We went to a second library. He could barely walk, so I entered alone and e-mailed the communiqué.

In the days that followed, I read the news, and it was funny to see speculation that was so completely off base: that at least a dozen people had been responsible, that it must have been an inside job, etc. People tend to think this stuff is much harder than it actually is. We did $12 million in damage—a big part of the $15,894,755.42 I'm supposed to pay in restitution. The expansion went forward—we didn't stop them—and insurance money paid to replace the buildings. But it didn't pay back the $13 million they lost in revenues. Call that the ELF tax.

And we were looking at a much larger canvas anyway, even if, as we later found out, we each had our own concept of what we were achieving. To some degree Avalon still believed in the political process. He thought we could shift the middle of the debate: By being so far at one extreme, we'd make the rest of the environmental movement appear more reasonable. That didn't really ring true to me from the beginning, and after the fallout from Vail—which turned out to be detrimental to local activism—it was even clearer. But even for Avalon, Vail wasn't really about Vail. It was about what we as a society are doing. It was about inspiring people, and that certainly did happen to some extent.

During the four years that I was most active with the ELF, there were parts of my life that were enjoyable. And there were parts that were not. Like being in a hotel room for days on end, everyone clad in painter's suits and face masks and hairnets and multiple layers of latex gloves, craned over tiny electronic devices and soldering irons. Nothing working out, and all of us sweating, frustrated, yelling at each other.

But then there was running around in the wilderness at night, and this incredible sense of being alive. You got to that point of just being totally in the moment. I felt connected to the natural world and really empowered in defending it. The emotion is hard to articulate—like we'd broken through the veil of what was possible. Like things didn't have to be the way they were. Some would call that idealism.