How To Find A Book From Your Past?

Somewhere between 1975 and 1980 I read a book in my gradeschool library.

At the time it had a huge impact on me, and I must have read it 10 or 20 times. I was a huge reading fan, and I've found most of my old gems again over the years, but this one is slipping away because I can't remember enough about it, and it makes me sad.

The book cover was some sort of purple/blue/? pattern. What I remember is that at the very start, the protagonist somehow finds a tunnel into the earth. Very early on he (or she?) finds a note in a room on the way which says something mysterious. They continue on and end up in some type of magical world. One specific thing I remember is that at one point in the story there are many elderly trees (or kinds of wood?) marked with plaques explaining their historical significance. I don't remember how the book ends.

This is just hopeless isn't it?

Throwing the bottle into the ocean just in case. Thanks for your time. :)
mark_lookabaugh (at) cox.net
mlookabaugh (at) powercosts.com
mlookabaugh mlookabaugh
41-45
Sep 8, 2012