About three years ago, UC Berkeley psychology PhD candidate Craig L. Anderson started investigating the components and implications of awe. Not the bad kind of awe—the sort you might experience if a mushroom cloud suddenly loomed on the horizon. But the good kind, specifically the variety associated with nature and all its manifold wonders: A sunset on a South Pacific atoll, icebergs calving from an Alaskan glacier, a hike through alpine meadows. Or in Anderson’s case, river-rafting.

Working through the Berkeley Social Interaction Lab, headed by well-known happiness expert and Cal psychology professor Dacher Keltner, Anderson began collecting data on veterans who participated in rafting trips down the South Fork of the American River. That included members of Cal Vets, Berkeley’s student veterans association, and participants with the Sierra Club’s Military Outdoors Program, an outreach effort headed by Robert Vessels, a former infantryman with the U.S. Army’s 10th Mountain Division who served combat tours in Iraq and Afghanistan and later took his bachelor’s degree from Cal in Middle Eastern studies.

As documented in California, that early work appeared to confirm that a nature fix was a pretty good Rx for post traumatic stress, instilling an immediate feeling of joy and inculcating an improved outlook over the longer term. Now, three years later, Anderson’s research has been completed and the results published in the journal Emotion. And the evidence seems clear: Nature heals, and it heals by creating a sense of awe.

Indeed, says Anderson, the lead author of the Emotion paper, awe isn’t simply one of the positive emotive responses that springs from exposure to nature: It’s the prime mover, the root from which all desirable emotional states such as happiness, contentment, giddy ecstasy, amusement, and so on, emerge.

Awe was the only emotion directly associated with nature. People would find contentment with their job, or gratitude from a stranger’s kind act, or joy at watching a favored sports team win—but only exposure to nature could induce awe.

“We conducted two studies,” says Anderson. “In the first, we tracked 124 veterans and underserved youth who went on either one-day or four-day whitewater rafting trips. Participants filled out diaries at the end of each day on their experiences and emotional responses, and we followed up with surveys on each of the participants a week later. We wanted to track six emotions: awe, amusement, contentment, gratitude, joy and pride.”

The second study employed a similar number of subjects, but focused on the role nature played in affecting emotion on a daily basis rather than pegging it to a rare but exhilarating experience such as a whitewater rafting trip. Subjects kept diaries on their quotidian routines, noting the degree of “nature” they experienced (e.g., from walking or hiking in a park) and their resultant emotional states.

In both studies, says Anderson, awe was the only element that predicted whether people would feel less stressed and more “healed.” Further, awe was the only emotion directly associated with nature. People would find contentment with their job, or gratitude from a stranger’s kind act, or joy at watching a favored sports team win—but only exposure to nature could induce awe.

“Only awe could predict whether people get better [from PTSD],” says Anderson. “There was no such relationship with other emotions. On the second study, we sent out online surveys that the subjects filled out every night for 14 days, and they also wrote narratives on the positive events of each day. We coded for different emotional responses, and on days when people wrote about experiencing nature, they showed extremely elevated levels of awe. There would be other positive emotions, but those always seemed to be maximized by awe. It’s basically like you come across an ancient redwood, and awe essentially stops the brain and allows the expression of other positive emotions.”

Jet Garner, a disabled Cal Vet who served as a corpsman with the U.S. Marines in Afghanistan, vouches for the power of nature-inspired awe. Garner was wounded by shrapnel during his deployment, suffering severely damaged nerves in his right arm. He returned home in 2011, and quickly retreated, he said, “to a dark place. I had problems with work, with friends. I broke up with my girlfriend. If I’d had a dog it would’ve died. I tried getting hobbies, but somehow I always ended up in a bar.”

Garner grew up in Tennessee and had always enjoyed the outdoors. Before his wounds, he had hiked, rock-climbed and fished. In the Marines, his permanent duty station was Hawaii; there, he took up spear fishing, a pastime he enjoyed immensely. But once his arm was injured, he dropped all those things.

He did pursue his education, however, enrolling in San Francisco Junior College after his service, eventually transferring to Cal, where he took his Bachelor’s degree in political economy and learned Mandarin through immersive courses. In some ways he got better—but not a hell of a lot better. The darkness remained, the pain buried more than ameliorated.

Then he participated in a 2015 rafting trip that Anderson monitored.

“The thing about that event that—well, really shocked me—is that normally vets get together over booze and just talk about their service time,” says Garner. “And that didn’t happen here. We were laughing, meeting each other’s significant others, and there was no alcohol. And no war talk. I realized I had been stuck in a loop. That we were all stuck in a loop.”

Anderson’s work got Garner thinking, especially as he considered the data that indicated the outdoors was actually helping vets heal.

“I realized I’d spent most of my adult life institutionalized,” he says. “Five years in the Marines, five years getting my Bachelor’s degree, serial girlfriends. Who was I? So I left my girlfriend, put my job opportunities on hold and basically immersed myself in nature. I’ve covered a lot of stuff out there hiking and backpacking, dealing with my PTSD piece by piece. So much happens neurologically when you have nothing to do but hike, just take step after step in beautiful, unspoiled surroundings.”

And he’s still at it. Garner has undertaken spectacularly ambitious backpacking expeditions in recent years, hiking the Pacific Crest Trail in sections, along with 480 miles of the Colorado Trail. He hopes to do the entire Pacific Crest Trail in a through-hike next year: “One way or the other, I’ll do something,” he says. “I’m not going to stop now.”

And he’s put ambitions for a career in international finance and trade aside, probably permanently. He’s starting a nonprofit outdoors company, RuckThru (a portmanteau of rucksack—the favored military term for a backpack—and hike-through).

“I’m still buried in all the paperwork,” Garner says, “but when I’m done I’ll be taking eight vets at a time on long-distance backpacking expeditions as an alternative treatment for PTSD. I have a sense it’s going to be my life’s work. If my primary legacy is that I took a lot of vets into the wilderness and maybe helped them with their issues, I’m fine with that. For me, it feels a lot healthier than my earlier plans of selling things to China.”

Like Garner, Vessels, the Sierra Club’s Veteran Volunteer Coordinator, says he knew from his own experience that the wilderness eased internal strife, “But it’s really great to see the benefits quantified, to see that the data supports what you intuitively feel. You can talk and talk about it, you can share anecdotes, but it’s good to have that peer-reviewed data for a variety of reasons.”

For Vessels, foremost among such reasons is changing the way things are done at the Veteran’s Administration. Instead of, or at least along with prescriptions for pain killers and anti-depressants, he’d like to see Veteran’s Affairs (VA) start prescribing sleeping bags, tents, whitewater rafting and backpacking trips.

“Something like that can be difficult to implement across the entire system, because it’s so large and each hospital is semi-autonomous,” Vessels says. “But it might be possible to at least get a pilot program going with the San Francisco VA. They’ve been one of the more progressive hospitals, and they’ve done a lot of work with mindfulness and yoga programs there.”

That largely jibes with Anderson’s plans. He’s currently conducting post-doctoral research at the San Francisco VA, and hopes to kick-start an initiative that incorporates nature-oriented therapies with PTSD recovery programs.

“The dream is to be able to say to veterans, to inner-city kids who are suffering, to anyone with PTSD, ‘Here’s a ticket to go whitewater rafting, or here are your hiking boots and a backpack—your co-pay will cover it,’” says Anderson. “Of course, if you go to a health care provider now and suggest something like that, they’ll laugh you out of their office. The work we’ve done to date is sound, but we need to do more research, and research is expensive. People intuitively know that nature is good for you, we’re showing that those intuitions are supported by hard data, but making the leap to policy and funded programs is difficult.”