As a retired California City Engineer I will say that it is too soon to know the solution. I could be a bridge, rerouting into the hillside or cutting out the slide in horizonal benches and rebuilding the slope. Not having seen it in person and without geotechnical and topographic studies I won't speculate on which it will be. California did relocate a short section of Highway 1 north of Pacifica by building a tunnel. This was done after repeated slope reconstructions failed in the same spot. Tunnels may someday come to short sections of the Carmel to Cambria highway because no one is going to close it permanently and nature will not stop washing it away.
