Finding The Cache (updated 12/28/13)
To find the cache you will need to find the actual location of benchmark AF3042 which is within 200 ft of the posted coordinates. Then project a waypoint bearing 40 degrees at a distance of 310 ft. You will not find the cache if you just project a waypoint from the posted coordinates!
The hide itself should not be too difficult, but I'm giving a higher rating because of the challenge in locating the benchmark and knowing how to project the right coordinates. Both the benchmark and cache can be accessed from the trail east of the railroad tracks (the former Old Dixie Highway). Do not trespass on railroad property - it is neither necessary nor legal!
What Is A Benchmark?
A benchmark is a point whose position is known to a high degree of accuracy and is marked. The marker is often a metal disk made for this purpose, but it can also be a church spire, a radio tower, a mark chiseled into stone, or a metal rod driven into the ground. Surveyors use these marks, but searching for them is a hobby for some non-surveyors. Some benchmarks are on private property which means you can't search for them. Benchmark data is stored in a mix of local and national databases. Geocaching.com has data for the main national database compiled by the National Geodetic Survey (NGS) dating from 2001.
Benchmark finds you log show up on your geocaching.com profile stats, but do not count toward your Total Finds.
Other Benchmarks In Or Near JDSP
AF3042, AF3027, AD3008, and AF3045 are just east of FEC railroad right-of-way and west of the Old Dixie Highway. Not all are easy to access and some only have scaled coordinates. Do not trespass on FEC right of way if you search for them!
AF0130 is the LORAN tower mast, which you can see from a distance. AF3047 is a survey disk at the base of the tower, but that area is off-limits to park visitors so don't search for it!
AF8748 is on Hobe Mountain and easy to spot from the tower boardwalk.
AF7533 is just outside the main park entrance. Park in the lot by the ranger station and walk out to it. Do not park outside the gate or on the road.
AF7532 is just outside the park ranger gate (next gate north of the main gate). That gate was the main gate for Camp Murphy. Don't park on the pavement or block the gate there and watch out for Spanish bayonet plants.
There are several benchmarks around the old cistern, but the area is fenced off so they may no longer be accessible.
You can check your projected coordinates with GeoCheck.