I learned land navigation in the military using a map and a compass, using the Universal Transverse Mercator (UTM) system rather than latitude and longitude. I’m old and stuck in my ways, and Sean plays along. Any coordinates I give for where rock art can be found are in UTM. For example, 557387, 4406636. The first number is the easting; the second is the northing, and it’s accurate to one meter on the USGS 1:24,000 maps. If you use a different system, you can convert the coordinates here.

You can find more about UTM here. If you use maps, UTM truly is a much easier system.

I still take USGS maps when we go rock art hunting, and I mark the spots where we find rock art on them. For those who like maps, I include both the USGS 1:100,000 and 1:24,000 maps for where the rock art is. However, there is something one must keep in mind when using these maps.

Every GPS system I’ve ever used gives coordinates, whether in degrees, minutes, and seconds latitude and longitude, lat/long decimal degrees or UTM, using the North American Datum (NAD 83) or the 1984 World Geodetic System (WGS 84) systems. Any coordinates I give will also use NAD 83 or WGS84 (which are virtually the same).

That said, it’s been my experience that most of the rock art is found in remote places, and the USGS has not updated the maps to NAD 83 or WGS 84. Most of these maps use 1927 North American Datum (NAD 27), which can be 200 meters or more off.

So, if you are trying to plot a coordinate on a USGS map from a GPS, your plot can be off. You need to convert the NAD 83 coordinates to NAD 27 coordinates. Fortunately, there is a website that does this for you.

Simply use the top drop-down box to select the system for your coordinates and the second drop-down box for the system to which you would like them converted. For example, the coordinates for parking for the Coyote Placing the Stars Panel in Nine Mile Canyon are East 557387, North 4406636 (usually written without the directions, 557387, 4406636). I would enter those coordinates into the top box and select UTM NAD83 Zone 12 (because all of Utah is in zone 12N) as the system from which I would like to covert. I then select UTM NAD27 Zone 12N in the second drop-down box and click on convert. The program gives me 557449, 4406430 as the proper coordinates for a map printed using NAD 27.

If I plotted the 84 NAD coordinates on the 1:24,000 map, it would be 62 meters east and 206 meters north of where the plot should be. For a coordinate next to a road or other recognizable landmark, this may not be a problem. However, for coordinates in the middle of the desert, one could spend a lot of time looking for a rock art panel that is a couple of football fields away.