The slope bordering the Magdalena delta and the adjacent outlier of the Andes has a complex morphology. This includes typical delta-front slope valleys directly off the Magdalena River and off its old mouths, bordered to the west by anticlinal hills and synclinal valleys, and to the north by fault blocks with a northeasterly trend. To the east, the slope has a concentration of mud diapirs rising mostly from between 400 and 750 fm (730 and 1,370 m). Farther east, a partly filled synclinal valley extends seaward from the Golfo de Santa Marta. Off the mountainous coast east of Santa Marta, a large submarine canyon winds down the slope almost to Colombia Basin. This canyon cuts through a large fault scarp, which forms part of the southeast margin of the basin. The sea-floor relief has been formed by a combination of complex faulting and folding, prograding sediment from the Magdalena with attendant formation of slump valleys, partial filling of structural valleys with the sediment, diapiric intrusion of plastic mud from underlying formations, and marine erosion producing a large submarine canyon. The source of the sediment that has excavated the canyon is unknown but presumably is supplied by streams entering the sea from a north outlier of the Andes.