Abstract Craters of the Moon National Monument (COM) basalts offer a reasonable analog to martian basalts, as they have elevated iron concentrations compared to traditional terrestrial analogs. Although secondary sulfate minerals on the evaporitic regions of Mars consist primarily of Mg-, Ca-, and Fe-bearing sulfate minerals, recent orbiter spectroscopic data have suggested Na-sulfate minerals may be present. Secondary minerals in the basaltic caves of COM in southern Idaho are white, efflorescent deposits in small cavities along the cave walls and ceilings and localized mounds on the cave floors. These deposits were examined using X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), Fourier transform infrared spectrometry (FTIR), and laser desorption Fourier transform ion cyclotron mass spectrometry (LD-FTICRMS). The secondary mineral assemblages were dominated by Na-sulfate minerals (thenardite, mirabilite) with a small fraction of the deposits containing minor concentrations of Na-carbonate minerals. Based on thermodynamic modeling results, formation of the deposits was attributed to leaching of basalt minerals by meteoritic water followed by evaporation of solutions. Such deposits could form under similar conditions in basaltic caves on Mars, making caves an excellent target for astrobiological investigations.