The Yilgarn Craton of Western Australia hosts a regional acid saline groundwater system and hundreds of ephemeral saline lakes characterized by complex acid brines. These acid saline lakes and groundwaters have pH as low as 1.4 and salinities as high as 32% total dissolved solids. The low pH formed by a combination of processes dependent upon the host rock lithology and mineralogy, climate, weathering, organisms, and time. Although these modern acid saline environments are relatively rare, they have both ancient terrestrial and extraterrestrial counterparts. Understanding acidification processes provides enhanced understanding of hydrosphere-lithosphere-atmosphere-biosphere interactions. These environments present evidence of new brine evolution pathways and suggest the potential for future intense acid brine environments.