The cache is NOT at the posted coordinates.
The trail in Middle Patuxent Environmental Area (MPEA) is approximately 2.15 miles in length, is in excellent condition, but is often muddy, especially down along the river. Terrain difficulty is 3.5 just because of its length. This is a great cache for kids if they are old enough to do the hike.
The listed coordinates, N39 12.755 and W076 55.111, are for the recommended parking area on Trotter Road, not the cache. Lizzie's Long Walk – Redux is a multi-stage cache where all the intermediate stages are within the MPEA. My dog Lizzie and I use to take this walk within the MPEA once or twice a week. The first six stages are on the well-marked trail, there is no reason to take even a step off of the trail. The trail will lead you down to the river and back. At the six stages, you will obtain some numbers, which after doing some simple arithmetic, will reveal the final cache location. Originally, the final was at the split rail fence along side Trotter. However, that was within 500 ft of a nearby Mystery cache. Hence, you will need to drive a few tenths of a mile from where you are now parked. The final will be less than 100 ft from where you can park.
Stage A (N39 12.743 W076 54.748): Let A be the number of Orange Disks on the post.
Stage B (N39 12.613 W076 54.426): Let B be the number of Arrows on the post.
Stage C (N39 13.036 W076 54.549): Let C be the number of Bolts on the right-hand railing Divided by 3.
Stage D (N39 13.110 W076 54.665): At this location there is a nature trail sign with a two digit number. Let D be the Sum of the two digits.
Stage E (N39 13.025 W076 54.901): At this location there is a bridge that has anti-skid metal plates. Let E be the number of metal plates divided by 2.
Stage F (N39 12.869 W076 54.870): At this location there is an informational sign with bullets (i.e. Big Dots) on it. The number of Bullets is a two-digit number. Let F be the Sum of the two digits.
As a checksum A + B + C + D + E + F = 30
The final cache location is given by N39 1F.XCY W076 55.YFZ where
X = A + B - D, Y = E - C, and Z = A + B
As a further checksum X + Y + Z = 15
I hope you enjoy the walk within the MPEA as much as Lizzie and I used to and I still do.