Lol just Google bud it should give you the directions and all

Construction began in 1938 it was completed in 1945 it was built for flood control

Behind Shasta Dam is Shasta Lake, which is the largest water reservoir in California. California is the most populous State in the United States. Shasta Lake provides irrigation for parts of the San Joaquin Valley, one of the most productive agricultural regions in the world. From Wikipedia: Shasta Dam creates Shasta Lake for long-term water storage, flood control, hydroelectricity and protection against the intrusion of saline water

You can at this time drive over the damn, but not stop on it. though it doesnt look like it because the way the cones are plced, but the guard will come out of his shack to check to make sure your registration is current, then wave you on.

There is no cost to take part in the tour. Be sure to show up a bit early to the visitor's center to get your ticket(s) for the tour, then walk to the middle of the dam, where the tour starts.

There's a tunnel from whiskey town lake that goes to Keswick ,never heard about your tunnel , I've been here since the mid 60's ,

The website has all the information. The free tour is great

Started construction in 1938, finished in 1945

518′ -> Shasta Lake/Max depth. 602′ -> Shasta Dam/Height. Maximum water depth -> 522.5 ft(159.3 m).