Pacific Gas & Electric Company went through six years of hearings, referenda and litigation to have the Diablo Canyon plant approved. A principal concern about the plant is whether it can be sufficiently earthquake-proof; the site was deemed safe when construction began in 1968, but a seismic fault (the Hosgri fault) had been discovered several miles offshore by the time the plant was completed in 1973. This fault experienced a 7.1 magnitude quake 10 miles offshore on November 4, 1927, and thus is capable of generating forces equivalent to approximately of those felt in the 1906 San Francisco earthquake.