Several risk factors are prevalent during early adulthood that can lead to cancer later in life. Emerging adults (EAs) aged 18-26 residing in rural areas of the United States engage in many cancer risk behaviors, especially sedentary lifestyles, poor eating patterns, nicotine product use, excess alcohol intake, infrequent sun protection, and inadequate uptake of the HPV vaccine. This application responds to RFA-CA-20-051, "Social and Behavioral Intervention Research to Address Modifiable Risk Factors for Cancer in Rural Populations." The goal is to improve cancer risk behavioral factors among diverse EAs aged 18-26 living in rural counties in the Four Corners states, a unique, underserved region, using a social media campaign designed with community advisors. EAs, including in rural communities, are heavy consumers of online content, especially over social media, and social media provide responsive, engaging, and low-cost platforms for distributing cancer prevention information with high dissemination potential. But, social media also circulate inaccurate, misleading, and harmful information. The specific aims of this research are to: 1) Develop a social media intervention for diverse EAs in rural communities via a community-engaged process that combines expert advice, user-generated content, and online instruction to communicate about behavioral cancer risks, cancer misinformation, counter marketing, digital and media literacy, and family communication; 2) evaluate the effect of a theory-based social media intervention on moderate to vigorous physical activity (MVPA), healthy eating patterns, nicotine product use, alcohol intake, sunburn prevalence, and HPV vaccination with the diverse population of EAs aged 18-26 in rural counties in AZ, CO, NM, and UT (Four Corners states) recruited from Qualtrics' survey panel and enrolled in a pragmatic randomized trial using a stepped-wedge design in which individual EAs will be randomized to 1 of 4 cohorts and receive the social media feed for varying durations in separate Facebook private groups; 3) test if improvements in EAs' cancer risk knowledge and beliefs, digital and media literacy skills, accurate cancer prevention information, and family communication mediate impact of the social media campaign; and 4) explore whether the impact of the social media campaign differs according to: a) level of EAs' engagement with campaign, b) cancer risk factors, and c) biological sex of the participants (as required by NIH). The research is innovative because it tests a theory-based, multi-risk factor approach to cancer prevention with diverse EAs in rural counties, an under-studied population, in a very popular new media. Social media may reach EAs more than interventions through other community channels (e.g., clinics, schools, and workplaces) and for lower cost in the geographically-dispersed, underserved rural communities in the Mountain West. The overall impact is extremely high because it will aid rural EAs in making informed decisions that reduce cancer risk factors and prevent cancer later in life and help EAs critically evaluate and resist misinformation and marketing that promote cancer risk behaviors.