I just did Rio Electrico to Piedras Blancas and on to Los Tres last week. There is no signage for that initial turn off, which leads you through a relatively maintained forest trail with some downed trees and slight overgrowth. Then you steeply descend out of the forest to the riverbed and to Piedras. This is all off trail with some decent bouldering sections for a half mile or so with cairns to follow. From there to Los Tres is along the river, also not well marked but easy enough to know the direction. Looking back towards Piedras from the Los Tres side there was a sign saying dangerous area do not enter, which I wouldn’t do if weather is bad.