Background: Rural youth face barriers to involvement in effective Science, Technology, Engineering, and Math (STEM) learning experiences, leading to persistent underrepresentation in STEM fields. Purpose: This study examined the feasibility of using mobile devices to engage rural youth in informal STEM learning (ISL) during free-choice, outdoor recreational activities. We assessed outcomes of a 10-month intervention related to STEM interest, identity, and future planning. Method: Fifty-four youth ages 12 to 17 completed monthly STEM challenges delivered via a mobile platform, aligned with connected learning and free-choice learning principles. Surveys measured pre/post changes in STEM supports, STEM confidence, and environmental concern; qualitative reflections explored meaning-making and identity shifts. Findings: Youth across sociodemographic groups reported quantitative gains in STEM supports, confidence, and environmental concern. Qualitative responses to reflection prompts indicated greater recognition of STEM in outdoor contexts and increased interest in STEM-related futures. Implications: ISL designs using mobile technology and grounded in inquiry, autonomy, and local relevance can foster meaningful STEM identity development in rural communities.