Manganese‐oxidizing microorganisms have been implicated in the deposition of manganese in dark manganiferric rock varnish coatings on desert rocks. For this study, a collection of bacteria able to oxidize manganese has been obtained from rock varnish samples from the Sonoran and Mojave Deserts. Two groups of organisms predominated among the isolates. One group was identified asArthrobacterspp. based on their rod‐coccus transformations, cell shapes, postfission division stages, and physiological characteristics. Another major group consisted of gram‐positive cocci tentatively ascribed to the genusMicrococcus. In addition, single isolates ofBacillussp.,Planococcussp.,Streptococcussp., andHyphomonassp. were identified as manganese‐oxidizing bacteria. Some isolates grew too poorly to be easily characterized and identified.