Observations at the site have led scientists to believe that the area was flooded with water a number of times and was subjected to evaporation and desiccation.  In the process sulfates were deposited.  After sulfates cemented the sediments, hematite concretions grew by precipitation from groundwater.  Some sulfates formed into large crystals which later dissolved to leave vugs.  Several lines of evidence point toward an arid climate in the past billion years or so, but a climate supporting water, at least for a time, in the distant past.