An extensive sabkha, 100 by 20 km (62 by 12 mi), caps Holocene siliciclastic tidal flats along the coast of Baja California in the northwest Gulf of California structural trough. This sabkha, bounded on the west by alluvial fans, is a complex of sand flat, saline mud flat, gypsum-halite pan, and supratidal mud flat subenvironments. The sand flat, transitional between the fans and the sabkha, consists of horizontally to wavy laminated sand washed onto the flats by sheetfloods from the fans under upper-flow-regime conditions. The sand flat passes into saline mud flats characterized by massive mud crowded with discoidal gypsum crystals grown within the sediment, destroying the layering. This intrasediment growth of gypsum is driven by evaporative pumping of brine from a shal ow subsurface brine body. A gypsum pan occupies a wide, shallow depression within the saline mud flat. After storm flooding (either marine or meteoric) the pan becomes a temporary saline lake with an algal mat overgrowing a siliciclastic storm layer. Precipitation of gypsum needles from the open lake brine and bottom growth of gypsum prisms produce a gypsum layer that mimics the algal mat topography. Evaporation of the lake leads to (1) vadose diagenetic growth of gypsum that distorts and polygonally disrupts the gypsum layers (2) deposition of a surface halite layer in the center of the pan. These layered pan deposits are the evaporites of the sabkha. Seaward of the saline mud flats are supratidal mud flats underlain by millimeter-thick laminites with deep prism cracks, sheet cracks, an scattered gypsum discoid crystals. Pervasive mud cracking during long periods of nondeposition completely disrupts layering, creating a massive arid "soil." A beach ridge separates this sabkha complex from the burrowed and ripple cross-laminated intertidal sediments.

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