Social media forms a mirror for the present and casts a shadow to the future. This exploratory case study focuses on the social media documents created by participants and organizers of the Burning Man festival, a temporary city of 50,000 inhabitants constructed annually in a remote Nevada desert. This ephemeral community develops through the collaborative, volunteer efforts of its citizens. Attendees generate all the content of the event, including large-scale sculptures, performances, and urban spaces. Event participants employ a spectrum of social media throughout the year to launch collaborations, develop and fund event projects, and maintain connections within their communities. This paper explores the role social media plays in the Burning Man community through a qualitative analysis of survey and interview data. The results suggest that social media serves as a documentary mirror and archival shadow which constructs and maintains the Burning Man festival, its culture, and its participant community. In view of this complex interplay between communities, documentation, and performance, the research advocates the expansion of archives to include social media documentation.