Investigation of a deep-water carbonate seep complex in the late Eocene Rock Creek section of the Keasey Formation, northwestern Oregon State, provides new data on marine carbonate seep occurrences in the formation. Methane seep carbonate bodies, with a diversity of seep-related invertebrate taxa are scattered across western Washington and the Rock Creek seep described here, together with the previously described Vernonia-Timber Road seep and Crinoid lagerstätte at Mist expands the Keasey Formation methane seep signatures. These three sites illustrate different points on a continuum from effusive to diffusive expulsion of methane and biotic chemosynthetic activity. Lithologic descriptions include a richly fossiliferous carbonate body named the Primary seep site, carbonite pipes interpreted as flow conduits comprise the Secondary Site, and minor pockets of blebby nodules is the Tertiary site, all within a 35 m stratigraphic section. Lithologic facies contain six named and characterized mollusk associations. Two are low-diversity with recognized chemosymbiotic bivalves and four contain opportunistic taxa tolerant of toxic geochemistry, severe oxygen depletion and nutrition potentially based on chemosynthetic microbial productivity. Analysis of ¹⁸O and ¹³C isotopes from the carbonate rock and from benthic foraminifera indicate that the methane-charged fluid flow sedimentary layers and probably burrow was driven by sustained microbial anaerobic oxidation of methane.