A comprehensive survey of lichens and lichen-associated fungi was conducted at Bryant Creek State Park during 18 field days from October 2020 through May 2022, documenting a total of 331 taxa. Despite areas of previous intensive logging and other impacts, the site contains an impressive level of lichen biodiversity, ranking among the highest lichen diversity recorded for a single site in the Interior Highlands and lower Midwest. Of the 331 taxa documented, there were 297 lichens (274 chlorolichens and 23 cyanolichens), 16 lichenicolous fungi (including one lichenized lichen parasite), and 18 non-lichenized, non-lichenicolous fungi often associated with lichens. Several of these taxa are new records for Missouri and/or the Ozark Ecroregion, and some are significant extensions of the known North American ranges for the species. Bryant Creek State Park constitutes a unique complex of extensive mesic sandstone ravine systems in a landscape context of contiguous intact or recoverable woodlands. In addition to the stunning scenic aspects of the extensive, seasonally flowing mesic ravines with diverse bedrock expressions, this system supports an unusual diversity of cryptogams, including lichens and associated fungi, with some uncommon and conservative species in abundances not known elsewhere in the Ozarks. Several small patch natural communities, such as seeps, glades, and bluffs of both sandstone and dolomite, occur at the park, further enhancing microhabitat diversity and supporting a diverse biota of lichens and associated fungi. With continuing, ecologically based management and restoration of degraded sites, as well as careful, sustainable development of visitor facilities and trails, this site will exemplify a distinct component of the Ozark landscape created by the characteristics of the region’s Roubidoux bedrock system, which is typified here more completely than perhaps any other area in the Ozarks.