Answer: There must have been a body of water there previously, maybe prehistorically.
Explanation: Gypsum forms when the right materials in a body of water come together and water evaporates quickly.
Gypsum is an evaporite, which means its crystals form during the evaporation of water. Gypsum forms whenever evaporation crystallizes the necessary minerals. In the case of "desert roses" gypsum crystals found around the world in arid sites, formation occurs with evaporation as the level of the water table changes. Gypsum can also be formed diagenetically by oxidation. This chemical reaction occurs when oxidation of existing sediments causes gypsum to form and replace other minerals in the sediments.
Huge gypsum deposits called beds were formed when ancient tropic seas became concentrated through evaporation. Gypsum crystals formed in the mineral saturated sea brine and sank to the ocean bed.
