score:4
Like JoErNanO suggests, you should look at websites of the bus hubs, called "Terminals". That being said, the info is probably out of date. I'd suggest asking the locals and arriving super early. Latin american transportation is not as punctual as what you'd expect from the first world.
Santa Marta doesn't seem to have a schedule.
Upvote:2
I use Rome2Rio to find local bus routes. http://www.rome2rio.com/s/Cartagena-Colombia/Barranquilla