Abstract Exobiologists are developing models and tools to recognize potential chemical, trace, and structural fossil evidence preserved on extraterrestrial bodies. It is believed that if life existed in the past elsewhere in our Solar System (and beyond), the most likely Earth analogues would be prokaryotes (NASA, 2001). This is due to the complex metabolic systems employed by the group, their small size, and their 3,500 million-year success record on Earth. Still, there is no consensus on how those lifeforms would be preserved in the extraterrestrial rock record. If they are preserved, it is still debated how we would be able to recognize them. As a first approximation, Earth-bound exobiologists have turned to "extreme environments" as potential analogues of ancient extraterrestrial conditions. One of the target environments occurs where hydrocarbons seep out onto the seabed sustaining an ecosystem dominated by chemosynthetic prokaryotes. This one-day field trip will visit an outstanding example of a fossilized hydrocarbon seep deposit—the Cretaceous Tepee Buttes of Colorado. The Tepee Buttes are a series of carbonate mounds that precipitated in the presence of seafloor methane release (Kauffman et al., 1996 ). In addition to the exobiology concerns mentioned above, methane release on the seafloor, whether through cold seeps associated with tectonic activity or destabilizing frozen clathrates, is increasingly viewed as an important geological phenomenon, potentially leading to mass extinctions, evolutionary events, spurring glaciations, and/or initiating greenhouse conditions (c.f., Kennedy et al., 2001 ; de Wit et al., 2002 and others). Modern methane (clathrate) reserves on the continental shelves are seen as a future target hyrdrocarbon source, though there are important environmental issues that need to be resolved (Haq, 1998 ).