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  • Writer's pictureDale Hill

California 2000 Center of Population

Surprise Survey Mark Recovery!


I always like survey mark recoveries that aren't on my radar, marks I stumble upon when not expecting to find anything or while looking for something else. I differentiate these finds from "drive-by" recoveries because of the element of surprise. I generally know about drive-by recoveries because they are marked on my map. These are opportunistic finds because I happen to be passing nearby. There can be a fine line between the two, as a survey mark not listed on the map could have a witness post that catches my eye, thus falling into the category of a surprise recovery.


Technically, if I had had my National Geodetic Survey (NGS) Data Explorer Beta Map open on my phone, I would have seen this marker as it has a Permanent Identification (PID) number assigned in the NGS database. The Beta map is a web-based interactive GPS map requiring an active internet connection. I don't usually have it open in remote areas with no connection, traveling through areas where I know there is a low concentration of survey marks or where it's impractical to stop.


Buttonwillow, California - Rest Area Recoveries


I was driving home today from San Francisco after a few days of camping, hiking, biking, and survey mark hunting. I've learned that the California Department of Transportation usually establishes survey marks at highway rest areas; consequently, I now check all rest areas for survey marks 🤣. Up to this point, all the survey marks that I have recovered at rest areas have been post-mile markers showing the mileage at that point from the beginning of the highway I am on.


Survey Mark Locations - Buttonwillow Rest Area Interstate 5

I was optimistic that I would find markers at the rest area on southbound Interstate 5 as I had made two recoveries at the rest area on the west side (northbound lanes). This rest area is three miles east-northeast of the incorporated community of Buttonwillow in the San Joaquin Valley in Kern County, California.


101 RESET & 104 RESET (Rest Area Interstate 5 North)


Unlike the typical post-mile markers I found in other rest areas, these were reset discs that appeared sequentially numbered. Generally, these marks are placed on the curb; however, these were set at the ends of concrete islands separating truck and automobile parking areas.


105 RESET & 106 RESET (Rest Area Interstate 5 South)



I pulled into the rest area, parked, and quickly found 105 RESET at the end of the center island, in a similar position as the markers I found Saturday on the west side of the Interstate. After making this recovery, I headed to the other end of the rest area to find 106 RESET when I saw a large brass plate mounted in a granite square on the center island!

CA 2000 CPOP (PID: DH6647)


8" Brass plate commemorating the California 2000 Center of Population

At the time, I didn't realize this was a registered survey mark and was excited about the surprise recovery. I prepped the plate for photographs and completed the recovery. I knew I had some research to do on this one when I got home!



Centers of Population


According to the U.S. Census Bureau, the center of population (COP) is a balance point. Imagine a flat surface in the shape of the United States and a standard weight representing each person counted in the census (and everyone weighs the same😉). The center of population would be the spot where that flat surface is in perfect balance.


The first census was conducted in 1790, and we have been counted every ten years since. Measuring and charting the country's population center change can graphically show how far and in what direction people are moving. From 1790 to 2020, the center of population has shifted westward over 900 miles, with a slight drift toward the southwest. To learn more about the historic centers of population, check out this page.


The center of population is also calculated for individual states and counties using the same concept. The "true" calculated center of population for California in 2000 is located five miles northeast of this monument in a cotton field between the communities of Shafter and Buttonwillow (the coordinates are engraved in the monument). They could have established the monument at the exact location, but having the monument in the rest area exposes more people to the history. You can read more about the dedication of the 2000 monument on the Mount Diablo Surveyors Historical Society's webpage: California's Center of Population Dedication.


New Goals


This was a fascinating internet rabbit hole to be drawn into! Discovery is a fantastic teacher; I continue to learn more about science, geography, different cultures, etc., by researching the history of survey marks I have found. Now, while traveling, I'll look for more of these commemorative centers of population markers. Not every COP will necessarily have a fancy monument like this one, but you never know. The more survey marks I recover, the more I realize I have yet to find!


By the way, this was the second commemorative survey marker I found on this trip. To score two in as many days, both unexpected recoveries, was incredible 😊 (I found the other in the Presidio of San Francisco and will cover that one in a separate article).




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