A 4x4 is definetly not necessary, I easily hitchiked solo to the Paso San Francisco and climbed the higher eastern cone from teh refuge in a 10 hour day( already well acclimatzed, I wouldnt count on doing it much faster than 10 hours) and then San Francisco the next day a 7 1/2 hour day. The route was pretty straight forward but some up and downs were hard to avoid as there is a lot of ground to cover to reach the peak.
Absolutley wonderful hike, definetly has the feelng that it is rarely climbed. If sleeping in the basic refuge at Paso San fransico it is very drafty, set up the tent inside or bring some fire wood from Las Grutas for extra warmth, and definetly a sleeping matress for the cold concrete floor.
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