Lake Mead - massive crystals of gray alabaster

Massive crystals of gray alabaster (a compact fine-grained variety of gypsum) and anhydrite crop out along Gypsum Wash. The gypsum forms from the concentration of salty water (rich in calcium sulfate). Gypsum occurs in ancient lake bed or playa deposits in the Muddy Creek Formation (Late Miocene). Gypsum is relatively soft and will flow slowly under pressure. Over time, it can migrate toward the surface along faults and fractures in the surrounding bedrock. This is a small gypsum diapir exposed in Gypsum Wash near milepost 2 along the Northshore Road.