This cache is not at the listed coordinates but may be found at N40 57.ABC W074 05.DEF.
The letters A-F may be found by going to the waypoint corresponding to that letter and reading the tenths part of the mile marker found there. There will be two mile markers on each sign post; use the one on the south side (that you'll see WHEN YOU'RE FACING NORTH).
For example, if you're at the sign post, facing north, and you see a sign that says 5.9, use the 9 for the digit.
The trailhead is at the given coordinates. Parking can be found right near by. The above picture is what you'll see if you follow the instructions correctly about looking at the sign post while at the given coordinates above.
Per the rules of geocaching, a Found It log must correspond to a signed logbook.
Happy caching!
You can check your answers for this puzzle on GeoChecker.com.
*** Congratulations to grschmid for FTF! ***