What is a “C-Monument”?

Roadways and their right-of-ways are marked in various ways. Originally, roadway rights-of-way were poorly marked, and as a result, changed quite a bit. These changes made travel sometimes rather confusing the roadway path may have changed before the map the traveler used changed. This sort of problem also cost the State quite a bit of money as they had to not only correct the problem, but also deal with the potential land costs of a new alignment.

Starting in 1914, the California Highway Commission came up with a plan to mark the right-of-way in a more permanent manner. Their solution – a “C-Monument”. While not the official name, which is simply “survey monument”, it aptly describes the marker. These monuments would be placed at the edge of the right-of-way at intervals along tangents (straightaways) and at curve points (BC and EC or Beginning of Curve and End of Curve). Optimally, these monuments would project about 6 inches above the ground with the C facing the roadway. At the top of the monument, a copper plug was placed to help guide surveyors.

Old C-Block State Highway Right Of Way marker from 1930.
C-Monument along a 1930’s alignment of US 6 in Red Rock Canyon.

The C-monument was actively placed and used for many years, though when it finally was out of use seemed to vary between districts. In San Diego County in District 11, for example, they were used along freeways constructed in the mid to late 1950’s. Los Angeles County, within District 7, seemed to stop using them sometime in the late 1930’s. Today, the monuments that remain are still valid survey monuments. While not placed anymore, Caltrans, as well as local agencies, still use them. As such, please do not disturb or collect them if they are still in place.  Finding them along a roadway also doesn’t automatically make it an old State Highway. Some counties also used these monuments as they were a part of the standard plans for any project that involved state or federal dollars.

Finding these monuments is actually quite simple. Typically, roadway rights-of-way ranged anywhere from 100′ to more than 300′. Find a curve in the roadway you are looking at and look for one on either side of the roadway about 50 to 150′ away from the centerline of the roadway. In mountainous areas, the uphill one tends to be easier to spot than the downhill side. Fence lines, power lines, and other similar features can be used to indicate the right-of-way edge. As they can still be used today as survey monuments, some are marked with paddles or other objects to make a surveyors job easier when locating them. Placer County uses a white “R/W” paddle. Caltrans District 9, at least in Inyo County, uses orange poles as location markers.

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