The 1989 earthquake caused the Central Freeway to be demolished, leaving a parcel of land unused. The California Department of Transportation gave the land to the City of San Francisco, which permitted the temporary installation of some cargo container-based buildings. You can read more about it here.
Now we know that the elevated freeways, the Central and the Embarcadero, were horrible for the city. They were dirty and noisy, blocked views, and took up valuable land, all for a few minutes of convenience for motorists. In their absence, lovely, lively urban spaces have blossomed. Funny how an earthquake can teach us about land use and urban planning.