At the above coordinates, you should find an information plaque, at ground level, entitled One Millionth Tree.
Use this plaque to obtain the required letters for the keyword to be entered into the checker.
If you enter the correct word, you will be given the final coordinates. The cache is only a short walk from here.
The letters:
Use the first line on the plaque. There should be seven words.
1) the first letter of the third word.
2) the second letter of the first word.
3) the second letter of the third word.
4) the first letter of the seventh word.
5) the eighth letter of the third word.
Now, form a word out of those 5 letters and enter it into the checker.
You can validate your puzzle solution with
certitude.