San Rafael is a city in Mendoza in West Argentina.
North towards Mendoza
There are two parallel routes to Mendoza joining in a roundabout after roughly 10km. Try to hitch on the further north RN143. The YPF gas station couple of hundred meters after the roundabout at the end of San Rafael is a good point to start.
East towards Buenos Aires
There's nothing really on the way from here to Buenos Aires. RN143/RN188 used to be the old road to Chile, there could be still people taking the full route. It might be faster to take the detour via San Luis on RN146. However, you will have to decide at the very start, as RN143 starts south of the riverbank of Rio Diamante.
South towards El Nihuil
Due to traffic, RP173 should only be taken one way, direction north. If you want to see the Atuel canyon, first go to El Nihuil via RN144 & RP180. Some tourists should be able to take you there and back through the canyon on the same day.
Definitely one of the toughest possible routes to hitchhike in Argentina. Especially after Malargue the route is getting worse and remote. If you want to travel RN40 all the way to Junin de los Andes, expect a week travel time. Further information in the articles of Malargue and Zapala.
San Rafael is quite widespread. There are two routes going north to Mendoza and two east to Buenos Aires. If you don't want to spend some time here, ask if you could get dropped off at the right exit. Otherwise, expect to walk some kilometers to the end of town.