We set of from Calama to attempt this confluence and first took a bus to Sierra Gorda. From here there is a road going straight towards the confluence and we hitchhiked along it. Down this paved road we went and finally we got to this barricade where the guy told us to get out of the car and talk to the guards. In our broken Spanish we couldn't convince the guards to let us hike towards the confluence (the city was el tesoro and it some mining city). We hitchhiked South back half way down the paved road towards Sierra Gorda. Here there was a road to the west that led to Caracoles. We got out and tried to hitchhike down this road for an hour or so but no one picked us up.
This point is tough man! It is in the middle of a scorching desert and may well be impossible without your own vehicle. good luck!!