Classic and Postclassic Maya of the northern Yucatán lowlands collected salt (halite) in the nearly continuous cienaga (swamp) that extends over almost the entire 340 km north coast of the Yucatán Peninsula. Evaporating ponds in the cienaga provided abundant, pure, continually replenished salt that was loaded directly onto cargo canoes for transportation west along the Gulf of Mexico coast to the Mexican highlands and south, behind the Caribbean barrier reef, as far as modern Nicaragua. Salt was the basis for a vibrant Maya economy at the time of the Spanish invasion. The perceptive 16th century bishop Diego de Landa made the logical, but incorrect assumption that the salt "in this marsh [comes] from the rain water and not from the sea, [which]… does not enter because of a strip of land the whole distance, between the marsh and the sea
.” In fact, de Landa's "strip of land" is the permeable dune ridge that extends along most of the north coast and through which sea water filters inland and then evaporates in the cienaga. Remarkably, both the dune ridge and the cienaga (with water as saline as 85g/l) overly an impermeable caliche layer beneath which fresh groundwater flows seaward into the Gulf of Mexico. This caliche layer is rendered almost perfectly impermeable by a process specific to the north coast and is an important reason why the salt collection system is effective. The north coastline has moved slowly inland during late Quaternary mean sea level (Qmsl) rise because the land slopes gently seaward. Meanwhile, the Yucatán groundwater table, which is controlled by Qmsl, seasonally rises to the land surface along a narrow zone south of the cienaga. Thus, any cracks in the caliche layer become cemented by CaCO3
precipitated from evaporating carbonate-saturated groundwater. The zone of cementation has moved inland as sea level has risen, maintaining the caliche layer as an efficient aquitard that effectively isolates evaporating saline cienaga water (above) from fresh groundwater moving seaward (below).
Viability of Maya technology of salt harvesting is demonstrated along the northern coast where artisanal harvesting occurs alongside vacation houses, in fishing communities, and in undeveloped areas. In the northeast, capacity of the natural system is demonstrated by a commercial plant that can produce 750,000 tons of salt annually.