Walk direction north west out of town past an YPF gas station, up a hill with a "no walking" sign (they don't care) until you hit a giant roundabout where the Ruta 174 starts. The exit of the roundabout you will take has a little police check point where they mostly check the people leaving the bridge, not entering it. Just be a chill hitchhiker, put up your thumb and stop that car or truck that will take you across the swamp road and/or bridge. If your driver is going to Rosario and you want to skip it and head to Cordoba, try getting out at the toll booth (peaje) before the bridge. Switch rides here to find one that goes to Cordoba. Aim for Villa Maria at the least, as you will pass many suitable gas stations on the way.