@ScribbleAddict Thanks. My grandfather was looking for underground water and used the clay he got out of the hillside to make ceramics. It extended about 60ft. into the hillside until it finally collapsed after some years of not being up kept and storms/earthquakes taking their toll. It's still there, but only extends about 10ft inward.

@Tait That's really cool. Those things must have made great forts!

@ScribbleAddict It was fun to mess around in. The inside basically looked like a mine shaft if the lights were on and was pitch black when they were off. (Yes, he actually ran electrical wires up there and had lights along the tunnel that could be turned on.) When we were younger and he was in good health we were not allowed in without an adult. Later on when he became sick no one really bothered to keep us out though.

@ScribbleAddict I don't have any pictures of the inside, but it basically looked like this picture except that all the supports were made from redwood. It just extended straight back as one tunnel. There were no side passages or anything. https://goo.gl/images/yjsjPG

@Tait That's super cool!

@ScribbleAddict Oh, and they did make great forts. There were a number of other burnt out stumps on the property that we were allowed to play in. I should go back and take some pictures of those some time.

@Tait We had paths all through our woods and we'd make forts under fallen trees, and among stands of trees that made a bit of a wall. The woods were where we did everything growing up. I used to imagine I was in the Redwall series, or Lord Of The Rings, or make up superheroes to be :)