Santa Rosa is reached from Jaén, the main city in the area. Shared transport (colectivos or combis) make the run when enough passengers show up, and the journey takes a couple of hours over roads that can be rough. There is no regular bus service; you will need to ask locally in Jaén about vehicles heading to Santa Rosa.
If you are doing a day trip from Jaén and continuing to Puentosillos, start as early as possible in the morning.