R., yes, you should report it! Let the police agency decide whether or not they want to investigate. I can think of no way that you could get in trouble and you'll have a load off your mind. Just tell them something similar to what you've written here. If you want you can write or send them an e-mail message. Be sure to include info on how to talk with you. This sounds a bit far fetched and they won't act unless they can ascertain thru talking with you that this has the possibility of being legitimate.
I've followed your questions and answers on this site and think of you as level headed. You have had many experiences from which you've learned much that is helpful for all of us. If you speak as well as you write they will take you seriously tho they may decide not to follow up since your info is 20 or so years old. I think you're military or ex-military. Law enforcement has a similar milieu. I suggest that you'll soon feel comfortable talking with them.
I'm not up on technology and so don't understand how you tracked the location using google earth. However, if you can track it, law enforcement can too. I don't think you'd have to be there.
Do you know what department or agency would provide law enforcement for the preserve? That is the agency to call, I think. If you don't know start with the county in which it's located. Ask to speak with a cold case detective. Expect to be questioned in detail or the opposite, to be put off. If that person won't listen, ask to speak to a supervisor.
One of the mom's suggested calling the FBI. I would start with the county or the preserve law enforcement but if they don't listen, call the FBI.
Sigh! What a memory to carry all these years! I understand your not telling anyone. Even without your family dynamics, I suggest that you could've been be too frightened and wanted nothing more to do with it. You could have wanted to deny ever having seen it, even. Lots of reasons to not tell anyone. Let go of the guilt, if you can.