National Oceanic and Atmospheric Administration (NOAA) 93

Science | Service | Stewardship Understand the Eart

Survey Mark Hunting

National Geodetic Survey Satellite 

Triangualtion Program, illustrating the idea 

of modeling the Earth. 

Courtesy NOAA Geodesy

Imagine bridges not meeting in the middle...

Airplanes landing next to runways instead of on them...

Ships frequently running aground...

This is just a glimpse of life without geodesy. 

What’s geodesy? It’s the science of measuring the size and shape of the 

Earth and accurately locating points on the Earth’s surface (and is pronounced “gee - ODD - ess - ee”). 

READ ON, and find out how geodesy can be a lot of fun!

Another way to think about geodesy is to imagine a world globe with a lot of 

pins stuck in it. Geodesy is about giving each of those pins its own “address” 

written as latitude and longitude. Why is this important? Because each of 

those pins can serve as a starting point for describing the location of any 

other point on Earth; just like when you want to tell someone how to get 

to your house, you give them a starting point that they know, like a road or 

a building. In the United States, these reference points are developed and 

maintained by NOAA’s National Geodetic Survey (NGS). 

Hang on, we’re almost to the fun stuff!

So where are all those pins stuck in the globe? They are everywhere—more 

than 1,200,000 in the United States!

Of course, they really aren’t pins. Instead, NGS uses permanent marks called 

“survey marks” (you may hear survey marks called “benchmarks,” but benchmarks are only one type of survey mark). Often, survey marks are marked 

with a metal disk like the photo below, set in concrete or bedrock:

Survey marks can also be stainless steel rods driven 

into the ground, drill holes in bedrock, bottles, 

pots, or landmarks visible from a long distance, 

such as a water tower, a radio mast, or a church 

steeple.

What You Will Do

Get information on the location and description 

of survey marks in your geographic area, and find 

out how to share your survey marking discoveries 

with the rest of the world! Courtesy NOAA Geodesy Collection
http://noaa.gov

Discover Your World With NOAA

94

Now for the fun:

Although the majority of benchmarks are located 

in plain sight, they are usually ignored by the 

general public. Many benchmarks haven’t actually 

been visited in a long time, and no one knows 

whether or not they still exist. So if you find one 

of these benchmarks, so you may actually be 

rediscovering long-neglected objects of American 

history!

Searching for survey marks is called “mark recovery” and is a lot like a treasure hunt (you may 

hear this activity called “benchmarking” but the 

correct term is “mark recovery”). Hunting for 

survey marks can lead to interesting places like 

high mountain peaks, deep woods, old buildings, 

bridges, and sometimes, ghost towns! You can 

enjoy the excitement of being the first to find and 

document a long-lost survey mark; write a log for 

your discoveries on the worldwide web; and if you 

find a survey mark that hasn’t been recovered in 

a long time, you can submit a recovery note, with 

your name, to the NGS website. Hunting for survey 

marks can be even more fun if you have a global 

positioning system (GPS) receiver. With GPS, you 

can go very close to the exact latitude and longitude of survey marks installed in your area. This 

is a kind of treasure hunt called “geocaching” 

(pronounced “GEE - oh - cashing”). 

Here’s how can you find out about survey marks in 

your area, and try your survey mark hunting skills!

What You Will Need

r Computer with internet access

r (Optional) Digital camera for photographing 

your discoveries

r (Optional) GPS receiver (this is useful for 

getting close to a specific survey mark, but 

the actual “find” is usually done by using 

very detailed location descriptions from the 

survey mark’s datasheet)

Warnings

1. Mark recovery should ONLY be done with an 

adult partner!

2. Many survey marks are on private property, 

and may be in dangerous areas. Be sure to 

obey local laws!

How to Do It

1. The first step is to find out what survey marks 

are located in your area. The easiest way to 

do this is to use the search engine on the 

geocaching Web site: http://www.geocaching.com/mark. This site also has lots of information and “frequently asked questions” 

about mark recovery. Enter the zip code for 

the area you want to search in the box on 

the upper right side of the page, then click 

on the “GO” button. Soon you should see 

a page listing benchmarks in the vicinity 

of this zip code. You can click on the PID 

number (second column from the left) for a 

description of a survey mark’s location, history, and logs from other hunters.

You can also get information for many survey marks from the NGS Web site. To recover 

the entire datasheets for survey marks, use 

the NGS Datasheet Retrieval Page at http://

www.ngs.noaa.gov/. 

a. Click on “Datasheets” at the top of the 

page. This will open the “NGS Datasheet Page.” 

b. Click on the “DATASHEETS” button on 

the left side of the page to open the 

“NGS DATASHEET RETRIEVAL PAGE.” 

c. Click on “PID”, then enter the PID 

number (from the geocaching.com Web 

site) for the survey marks, then click 

the “Submit” button. This will open a 

window titled “Station List Results for: 

---”

d. Click on the PID number in the white 

window, then click the “Get Datasheets” button. This opens the complete datasheet for the survey mark 

you selected.

e. At the bottom of the Datasheet is a 

section titled “Station Description,” 

which gives very precise instructions 

for finding the survey mark, starting 

from easy-to-find landmarks (such as 

a public building or the intersection 

of major roads). This description also 

includes information about things that 

may make it easier to find the survey 

mark, such as:

“30 FEET SOUTH OF THE CENTER LINE 

OF THE ROAD, 23.98 FEET WEST OF 
National Oceanic and Atmospheric Administration (NOAA) 95

Science | Service | Stewardship Understand the Eart

BENCH MARK 33 A (USGS), AND ABOUT 

2 FEET LOWER THAN THE ROAD.”

or

“8 FEET SOUTHEAST OF A GATE IN 

AN EAST-AND-WEST FENCE, AND IN 

THE TOP OF A LAVA ROCK. A UNITED 

STATES GEOLOGICAL SURVEY STANDARD 

COPPER NAIL AND WASHER, STAMPED 

5240.4.”

2. Now see whether you can locate some 

benchmarks. Read the location descriptions 

carefully, and try to start in areas that are 

familiar. BE SURE TO DO THIS ONLY WITH AN 

ADULT PARTNER!

When you find a benchmark, you can take 

pictures, but that’s all! Never disturb or 

move a benchmark, even if it appears 

to have been damaged. Remember that 

benchmarks are important, they are public 

property, and are protected by law. 

You can also log your find on the geocaching Web site. See http://www.geocaching.

com/mark for instructions.

If the location for survey marks is described as something like a radio tower, 

church steeple or smokestack, the top of 

these structures is usually the survey point 

(there is not normally a separate disk or 

other mark). Do not climb these structures! 

Just log your find, and take the structure’s 

Members of a 1922 geodetic survey expedition. Until recent advances in satellite technology, namely the creation of the Global Positioning System (GPS), geodetic surveying 

was an arduous task best suited to individuals with strong constitutions, and a sense of 

adventure. Courtesy NOAA NOS Geodesy.

picture (from the ground!) if you have a 

digital camera. 

Want to Do More?

You can find out more about geodesy at NOAA’s 

National Ocean Service Web site:

http://oceanservice.noaa.gov/education/kits/geodesy/welcome.html

The official geocaching Web site http://www.

geocaching.com has lots more about mark 

recovery and geocaching.