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A 10-m-long core was recovered from the coastal flood plain on the eastern margin of the Gulf of California (Bahia Kino, Sonora). Sediments were analysed for loss-on-ignition, magnetic susceptibility, pollen, diatoms, ostracodes and foraminifera. Three levels were dated by C-14. The combined data suggest that the site was flooded during the middle Holocene as sea level increased. At about 6600 yr BP the area was a freshwater to brackish marsh dominated by Typha domingensis and Cyperaceae. Freshwater to brackish conditions suggest the presence of a local source of freshwater during this time and therefore a climate wetter than present. Continued rise in sea level was associated with an increase in depth and salinity. By c. 6350-6250 yr BP, the coring site was an inner lagoon, by c. 6125 yr BP a central lagoon and by c. 5900 yr BP the site was close to the mouth of the lagoon (lower lagoon). Lower lagoon conditions persisted until the top of the record, showing sea-level stabilization; which was followed by the formation of the dune ridge that presently separates the coring site from the sea.