In this paper we report our investigation into how using and interacting with a local festival mobile app enhanced users' festival experiences and connected them to other local users and their community. We explored the relationship between users' perceived basic affordances of mobile technology, perceived opportunities of the festival app, and three elements that sustain the local community-attachment, engagement, and social support networks. Based on the usage logs of 348 active users, as well as survey responses from 80 users, we present a mobile-mediated local community framework and found that engagement is a key mediator of mobile experiences and facets of community.