Historical cartography is increasingly being used for the study of coastal evolution, but less considered are coeval descriptive sources as well as exploration reports that accompany the construction of maps. Herein, these issues are considered when analyzing the chronological model of the Rio Sinú mouth and Cispatá bay evolution before the Tinajones delta formed (around 1942–1943) as it is established in the literature. This study is based on the examination of about 500 manuscripts or printed maps produced from the 16th century to 1937 (the last one before the Tinajones delta was formed) in which the Morrosquillo Gulf, the Rio Sinú terminal course, the Mestizos headland and Cispatá bay are represented. These maps were compared with coeval descriptive sources. Several maps are not based on new topographic surveys but are more recent elaborations of the original documents, while others include updates of only limited portions of the area and simply replicate or mix a drawn coastline, at best, tens of years before or, at worst, centuries before. A synchronic and diachronic comparative analysis of these documents was performed, and, out of these maps, only three were found to be reliable for the morphological reconstruction of the area. Many of the remaining maps turned out to be full or partial copies of the originals, so they attribute the wrong date to the described coastlines and water depths. These findings led to a new model for Cispatá bay evolution with respect to that proposed by previous scholars using some of these maps. In particular, some river mouths and coastal morphologies were backdated, and bay infilling proved to be far faster than described before. Written documents demonstrate that this process was triggered by inland slope deforestation.