The BILBY Geotrail
Basic Information for Locating Benchmarks Yourself
CHARLES ADAMS
THE GEOTRAIL
The Maryland Society of Surveyors (MSS) welcomes everyone to participate in this statewide trail which showcases the different “Benchmarks” used by surveyors and which geocachers enjoy finding. The BILBY trail will include a total of 20 cache locations with geocoins awarded at different levels of caches found.
To most non-surveyors any brass disk they find is a benchmark, however not all benchmarks are created equal. There are approximately a dozen different types of benchmarks, and this trail will introduce you to 5 of the most common. Azimuth Marks, Triangulation/Horizontal Marks, Reference Marks, Special Marks and Bench Marks also known as Vertical Marks.
One MSS geocoin will be awarded when 3 caches are found from EACH of the five different types of marks (15 total finds). We have a limited amount of National Oceanic and Atmospheric Administration geocoins that will be awarded to anyone finding all 20 BILBY caches. Be sure to record the code word from each cache to qualify for geocoins.
To claim your geocoin(s) use this link to access the decoder. If multiple people share one geocaching username, only single coins will be awarded per user.
First of all, we will refer to all these marks as “Control Stations” since the word benchmark really pertains to just one type of control station. Next, we will use “Bench Mark,” with two words, since that is the way the National Geodetic Survey (NGS) defines it and the NGS is the federal agency that maintains this network of control stations.
While Geocaching.com no longer allows you to find and record these in your geocaching statistics, you can still post your finds on Waymarking.com and the NGS would welcome all finds or DNF’s to be recorded in the Survey Mark Recovery section of their web site. The NGS also has an interactive map located on their Map Page to help you find them.
Here are the five types of Control Stations and locations in the BILBY Geotrail:
HISTORY AND WHY THE NAME BILBY
The first set of Control Stations were placed around 1816 when Thomas Jefferson established the “Survey of the Coast” with the mission to map the eastern coastline of the United States. Since boats were the main method of transportation and how to get goods to the citizens of this new nation, accurate maps were needed to identify rivers, bays, harbors, shoals, light houses and any other navigation aids to keep commerce moving safely.
The only way to make measurements, until GPS was invented over 200 years later, was by direct line of sight. Measuring from hilltop to hilltop was a way to cover large areas quickly, however since the hills and mountains were mostly forested, they needed a way to get above the trees. Lumber was obtained either from the forest itself or purchased at a nearby lumber yard to construct towers. Some towers were constructed over 100 feet tall.
Jasper Bilby (1864-1949), who this trail is named, was a surveyor and geodesist that worked for the U.S. Coast and Geodetic Survey. Jasper (Click Here for more information) saw the enormous amount of manpower and cost to build these towers which were typically left behind, due to the time and manpower to dismantle then transport them to a new location. He noticed the steel windmills used by farmers to pump water and thought he could do something with that. He developed a tower within a tower system, so the survey instrument was on one tower and the operator stood on another. That way as the operator moved around to take readings it did not affect the stability of the instrument. The inner and outer towers were color coordinated and bolting the sections together made assembling and disassembling easier and faster.
THIS STATION
A BENCH MARK/VERTICAL control station is one that has a very accurate elevation as referenced to established datum, such as sea level. This type of station is one of the two most common stations used by surveyors. All stations in the NGS database have a unique two-letter, four-number label known as a permanent identifier or PID as names of stations are frequently repeated. Clicking the link below, after the station name, will take you to the datasheet which has a lot of information about this mark.
CHARLES ADAMS (PID DH7944) was set in 2005, by the National Geodetic Survey. This is the newer type of Bench Mark and being a stainless-steel rod driven to refusal. This is more stable than the older brass disks set in a concrete monument which are about 3-4 feet deep. The station name "CHARLES ADAMS" is stamped around the rim of the flange-encasement and "ACCESS COVER" is on the lid. It is not uncommon for the lids to get lost. This marker was also measured to get horizontal coordinates.
THE CACHE
The posted coordinates will take you to the Charles Adams stainless-steel rod, with access cover, as shown in the picture above and the focus for this BILBY cache.
Please take a picture of the control station with a signature item and post with your log. While this is not required, it shows your appreciation to those many volunteers who helped create the BILBY trail.
After viewing the marker at the posted coordinates, make your way to headstone given in the additional waypoint. You will see an upright headstone of a man whose initials are RT that served in the US Army.
To get the coordinates for the final, find the following:
A=Number of letters in his last name
B= Second number of his birthday
C=Sum of numbers in the day of his death date
D= Last digit in year of his birth
X= Sum of all shown digits in the date of his death
Y= Sum of digits in the day of his death
Z= Second digit from left in the year of his birth
Final coordinates are: N 37° 5A.BCD W 75° 50.XYZ
The final is a short walk away.