At this point a ridge carrying Marin and Los Angeles Avenues blocked the way.

After investigating (1) a route around the ridge and (2) a cut through the ridge with bridges over it, it was decided to use the route of the cut but make it a tunnel instead, under Marin and Los Angeles Avenues just west of their intersection with The (Marin) Circle.

To accomplish this, a temporary wooden trestle was built along Henry Street with tracks for the construction trains which was subsequently filled in with material excavated from the tunnel cut.

[6] The railroad was completed in 1911 and inspection trains were run at the end of that year, with service beginning January 1, 1912.

Service was extended through the tunnel to a new terminal at Solano Avenue and The Alameda on December 6, 1942.