Lençois Maranhenses National Park, a coastal dune field (measuring some 155,000 hectares) that is flooded with freshwater lakes during the January to May rainy season. Strong prevailing winds from the East mobilize the barchan dunes during the dry season and, combined with the equatorial sun, evaporate the lakes and prevent permanent vegetation from taking root. The dunes are composed of quartz grains that are eroded from the granite and washed down from the Parnaiba River and then carried north by ocean currents before being deposited on the coast of Lençois Maranhenses. The name means "bed sheets of Maranhão Province", as from above they resemble undulating sheets of pure white.
Photos of small single-family homesteads in Baixa Grande, one of the two isolated oases in the center of Lençois Maranhenses. People here live mostly off coastal fish but also raise goats, pigs, cattle, and chickens. The soil is too sandy for agriculture to be very successful.