Shasta Lake Dam Tunnel
This tunnel is near the base of Shasta Dam. You take an elevator from the top of the dam to the base, my twin sister Sharon and younger sister Betty Lou and I walked through the tunnel and out the backside of the dam. If you were to stand at one end of the tunnel and clap your hand the sound will take about one second for the sound-wave to bounce off the other end and come back, sound travels at 1,126 feet per second. This may give an idea of how long this tunnel is. By the way, I wasn't at the end of the tunnel yet when I took the picture.
(view on black)
Below is an illustration of the elevator shaft and tunnel through the dam