Could the abundant sulfate salts on Mars contain microfossils and/or viable microorganisms? Here we report a variety of microorganisms trapped both as solid inclusions and as potentially viable halophilic and acidophilic prokaryotes and eukaryotes within fluid inclusions in Mars-analog gypsum. We have documented pennate diatoms, green algae, and prokaryotes in gypsum precipitated from acid (pH 1.8–4.6) saline (5%–28% total dissolved solids) waters at Salars Gorbea and Ignorado in an active volcanic terrain in the high Andes (4000+ m) of northern Chile. These salars are strikingly similar in geology and geochemistry to Mars. We propose that this discovery should serve as a model for fossilization of possible life on Mars and may inform methodologies used in future missions to Mars. Furthermore, the potential long-term viability of microorganisms within fluid inclusions in gypsum suggests the possibility of a living, yet isolated and likely dormant, microbiological community on Mars today.