This is the only discussion of the tunnel option in the 1986 Final Environmental Impact Report:
This alternative was proposed by the Sierra Club in 1973, and would go through San Pedro Mountain (Exhibit 32). Portals would be located at Green Valley and on the north side of San Pedro Mountain.
This alternative was withdrawn from active consideration because the tunnel would cost an estimated $100 million. In addition, a tunnel would have to be 2 lanes in each direction to provide access for emergency vehicles in the event of an accident or stalled vehicle.
Exhibit 32, a map included in the original document, is not reproduced here.