#94 Shovelbums Guide Part 15: The Smithsonian Trinomial System

When I was on my first professional archaeological dig with a CRM company I saw many things that puzzled me.  The first one was the grid they had set up.  I didn’t understand why they weren’t using latitude and longitude.  At that point I’d never heard of a UTM coordinate.  What kind of crazy system measures in meters and gives a unit coordinate of 1057 mE / 1062 mN?  Ah, the naiveté of inexperience.

The other thing that no one ever bothered to explain was the nationwide numbering system used for sites in the United States.  It just looked like an indecipherable string of numbers with an underlying structure that I just could’t make out.  Even if you’re relatively new in the field you’ve seen the numbers.  They look like this:



Recognize them now?  What do they mean?  I’m going to cut to the chase for the *tl;dr* crowd.  The first number represents the state, the letters are a two-digit code (sometimes three) for the county, and the last numbers represent the number of sites that have been recorded in that county.  When you ask your state archaeologist for a site number, the last set of numbers will represent the total number of sites recorded within that county (give or take a few - you may not have checked your email before they issued more numbers to someone else).

The state numbers run from 1 to 50.  The District of Columbia, American Samoa, the Federated States of Micronesia, Guam, the Marshall Islands, the Northern Mariana Islands, Palau, Puerto Rico, and the Virgin Islands do not get a number (who knew we had so many territories?).  The numbers mostly go in alphabetical order.  The exceptions are Alaska (49) and Hawai’i (50).  They weren’t states when the system was devised.

The Smithsonian Trinomial number was devised and perfected over a number of years by the Smithsonian’s River Basin Survey (RBS).  The RBS operated in a number of states and needed a comprehensive system of designating new sites.  The River Basin Survey started in 1946 and by the end of fiscal year 1947 in the Missouri Basin, 376 sites in seven states had been recorded.  Paul Cooper, an RBS staff member, was instrumental in devising the first incarnations of the system between 1946 and 1947.  The early system was based on an even earlier system that was used in Nebraska during the 1930s for WPA (Works Progress Administration) projects.  Other states were using a system similar to Nebraska for WPA fieldwork but none were identical.  Carl Miller, also an RBS staff member, added county codes for several southeastern states in 1958.  He was following some state universities and historical societies that had already incorporated the county code.

Although the RBS program ended in 1967, individual SHPOs continued to assign site numbers based on the Smithsonian Trinomial System.  Now, all fifty states issue site numbers [see the update below] a number of states issue site numbers using that system.  A lot of spatial data can be determined just by being able to decode the Smithsonian Trinomial.  Think about it.  Without knowing anything about a site you can narrow its location down to the county level in a matter of minutes.  I wish everything in archaeology worked so well and was so universally accepted.

I’d like to thank Rose Chou from the National Anthropological Archives (I didn’t even know such a thing existed) at the Smithsonian Institution in Maryland for contributing most of the information in this post.  I attempted, several times, to find historical information online about this subject but came up empty handed.  Believe it or not, it’s not even on Wikipedia.  If I had a hard source for this post (aside from an email) I’d write the entry.  Maybe someday.

Hope you’re smarter now!

See you in the field.