Looking good!
There's the glacial erratic! Not sure what that is? Check out the Glossary. You're not quite at the Y-intersection yet, so keep going.
Clues
Letterboxing began in Dartmoor, England, in 1854, when a guide named James Perrott left his calling card in a bottle at Cranmere Pool. To begin, pretend you’re James Perrott leading a group of hikers through the moors and find the trailhead at the easternmost point in the parking lot. Follow the trail until you come to a T intersection. Turn your compass South and continue on the trail marked with blue blazes.
The original Cranmere Pool calling card bottle was later replaced with a tin box, and later, a notebook was added for visitors to sign. Eventually, a rubber stamp was added and it became what we now know of as a traditional letterbox. Pass a vernal pool on your left and a glacial erratic on your right. When you reach a Y intersection, go west 55 steps to a snag on your left. Look behind the snag for a triple-trunked tree. Behind this tree you’ll see the telltale signs of the letterbox: Cranmere Pool. Please use green ink. Please re-hide well!