"The Bolivar geosyncline extends through coastal Ecuador and Colombia from southwestern Ecuador to the Golfo de Uraba. Six cross-basin highs separate the deeps within the trough. Marine sedimentation began in the south in the middle Eocene, gradually encroached northward, and continued intermittently on into the upper Miocene. Several unconformities of varying importance are present. Post-Miocene sedimentation is mostly non-marine."