Background: Skepticism of therapy and stigma are significant barriers for veterans with mental health issues. Therapeutic adventure shows promise in addressing veterans' mental health needs while circumventing the stigma many veterans face in initiating treatment. Purpose: Given the small group model of therapeutic adventure programs, such programs may be ideal to provide social support for veterans and reduce mental health symptomology. The present study investigated: can a brief peer-led therapeutic adventure program modify veterans' mental health symptoms? Methodology/Approach: The study's sample included 56 participants attending one Sierra Club Military Outdoors trip lasting at least three days and two nights and involving camping. Participants completed study measurements assessing depression, anxiety, stress, Post-Traumatic Stress Disorder symptoms, substance misuse symptoms, and suicidality at pre-trip, post-trip, one-month post trip, six-months post trip, and 12-months post trip. Six-month and 12-month post-trip data was collected during the COVID-19 pandemic. Findings/Conclusions: Results indicated significant reduction in mental health symptomology from pre-trip to post-trip, but showed few longer-term changes in mental health symptomology. Implications: The present study's findings are consistent with research suggesting improvements in overall psychological well-being immediately following a nature-based intervention and suggest the need for on-going, community-based interventions to support optimally military veterans' mental health.