Jump to content

City Monuments


Recommended Posts

On my first benchmark hunt the other day, my GPS led me to the middle of an intersection where a "City Monument" was placed. I thought this was the benchmark so I logged it and left only to discover that this was in fact not a benchmark.


This plaque is a small 6x6 inch (approx.) square with a small square hole in the middle and reads "City" towards the top and "Monument" towards the bottom. I've tried Googling these and can't find out any info. I've even seen a few more while driving. Anyone have any idea what these are or what they're used for? I live in the bay area and tried the CalTrans website but I didn't find anything. Any help is appreciated! Thanks.

Link to comment

I've observed that in many urban areas the benchmark is often incased in a miniature manhole-like box, presumably to deter vandals. I've seen them labeled "survey," but certainly "monument" is also a term that might be used.


It would be helpful if you would give the PID you were looking for, and you might carefully read the description to see what specifically you are looking for. Not all benchmarks are the familiar benchmark disks.



Link to comment

Many cities place survey monuments labeled as such. They may be used as geodetic or other survey control, or simply be used as centerline monuments. It is not uncommon for municipal survey control (or control from other agencies) to be placed in covered monument wells, particularly when they are placed in city streets. The wells are used for protective purposes and can be found with round, square, and triangular covers that either lift off or are hinged.


This is from the Solano County Department of Public Works Standard Plans.




- Kewaneh

Link to comment



You may find that in many cities and municipalities, there is a monument of some kind, in the center of most intersections. They were placed there by the municipality and there is likely a lot of information ascribed to them based on different projects down through the years. Planning, Engineering, Water, Sewer, Streets etc... They may be either or both a known point of location and elevation. Most often, they were placed to represent centerline of road, as based on the original design. Sometimes things change but the control remains where it is as there is a good bit of info described by it, from the past, and it still serves as a place which new things can be described, whether as offset or otherwise. Now that you know, you will likely see some derivative of these everywhere. Some may have been used by Geodetic Surveyors, as a borrowed monument (using a monument already found to be installed and permanent enough). Some you may find here at geocaching, but that would be more an exception that the rule.


Depending on the city, some engineering departments do list their survey control online, but again, that won't make it a game piece for here on geocaching, remember to check here first for those that are loggable here.


Enjoy, Rob

Link to comment

Of note:


On the second drawing Kenewah has kindly submitted, I would like to call attention to the section view.


Though this is a typical installation of this monument, there are variations so don't be surprised if this is not exactly what you encounter.


First I would like to touch on the safety aspects that go with this particular monument type. This is the type specified for placement in the street, so should you be interested in one of these, you too will also be in the street. I just want to remind those who may want to look inside that you will likely not be able to get the cover off with your bare hands, It will require a tool, and while you are trying you are in traffic and exposed to all the hazards which go with the territory. Quite Frankly you can Die trying to fool with it from contact with traffic and I know, make that used to know several people who have and are no longer here. Should you choose to have a look, Don't do it alone, two friends looking out for traffic are better than one, eyes and ears are important here, and the requisite safety gear you would see any road construction crew member wearing would not be a bad idea. Often we surveyors do not wear a hard hat unless we are working where one is required, but always a vest. Always.


Second, down through the years there have been variations on the theme used for this type of monument. Some Are just as you see, others have just a rod and no concrete around it, some have other things. Vaguely put I know but just trust me. Hubs, rusted nails and rotted wood, etc... On many, if they are old, the monument cover itself has likely been jackhammered out of the pavement after road resurfacing operations to reset it to the current level of the street as that may be the specified method in that jurisdiction, or a ring may have just been placed to lift the cover higher in others. Sometimes the crew raising utilities do not perfectly center the cover so you may find odd settings that way as well. I won't go into the method of Madness and other reasonings but this is common stuff to see when taken as a whole, so you may find that the survey marker under the monument is a good bit deeper or in other offset manners than the section view will show.


These also often fill with dirt and the dirt would have to be moved or removed to find the rod marker in there. Leaving the dirt in the road is bad form so if you must remove the dirt, try to leave no trace when you finish.


In my spare time I usually avoid bothering with these due to the lack of safety involved in trying to recover them properly. I can't see traffic while standing on my head. I have all the right stuff at work and can set up the proper traffic control. Interestingly though I have recovered a few in my life that were not there due to utility construction removal, where they put the monument cover back in the street after digging the monument up in construction to facilitate themselves. The hope on their part would be that the cover will put the inspector off the trail that there was a marker removed and they will sign off on it. All looks well but the next crew who needs to use the point will find nothing and the construction company is long gone. All the richer for not having paid to have the point re-surveyed. It happens. Other times finding the station covered with asphalt or concrete... And so the big thing to remember is that the monument cover is not the monument, the place under the lid is not always what you might think it is supposed to be and the location is often a dangerous place to be.


Good luck and safe hunting,



Link to comment

I'll second all that Evenfall has said. Simply put, don't go looking for benchmarks in the streets. It is VERY dangerous. Every surveyor and road worker can tell you horror stories of irate or unaware drivers. It's best not to try to experience these horrors for yourself.


I posted the images of the monument well plans only as a way to explain and describe what many benchmark hunters have found at one time or another. Not as encouragement to open them, particularly when they are in a roadway. Questions about the wells (Is this the mark? Is the mark underneath? Can I open it?) have appeared in this forum many times over the past few years, and the images I posted of the standard plans are intended to answer some of those questions.


- Kewaneh

Link to comment

The last two poster have given a wealth of information. I'm not sure why you would want to see the centerline monument in the handhole anyways. These are not typically the "benchmarks" that are referred to on this website anyways (at least not in my area).


I can tell you, for example, when we were surveying a church in Norwalk, CA I was bent over cleaning out the monument well (we had traffic control cones out, etc - and we were both wearing bright orange reflective vests in the middle of a clear day) when my partner in crime yanked me out about 10 feet quickly. I was taken by surprise but when I realized what was happening there was two police cars that were having a high-speed pursuit with an individual who wasn't cooperating, and drove right over where I WAS kneeling.


I know from experience that I wouldn't open one wearing street clothes by myself unless you provided a pot of gold :rolleyes:

Link to comment

Here's one that I know of - GU4200. It's located in the middle of the busiest intersection in town. One of the roads is a State Highway. When we occupied it, we had a crew of four. Three of us were in the intersection (with signs, cones and lights; the works) with one of us cleaning out the hole while the other two watched the traffic.


I don't have any pictures of the mark itself (*bad benchmarker*) but I should get some later this year. Another project in the area will get me out to it again.


- Kewaneh

Link to comment



It is not so much that C/L monuments are on this site per se, But when the Geodetic Surveyors needed a point someplace, and a city monument was handy, they often used it. When they did, and did very intermittently, they wound up in the NGS Database. I have noticed that they either used it for to turn angles for third order, or they some how decided to piggy back it in as an RM to a nearby mark and then turn angles on it for extra positions.


In any case, that is how they seemed to wind up as Geodetic markers, otherwise, they are not NGS property, and is why we only happen across them from time to time. Most C/L Marks, Likely more than 99% of all of them when taken as a whole, Nationally, are not in this database.



Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...