This little monument marks a point, surveyed under the auspices of the National Geodetic Survey (NGS), whose position and elevation are known with a high degree of accuracy. There are hundreds of thousands of such markers around the US, and, as part of the National Spatial Reference System, they can be used as benchmarks to determine the exact location of other points of interest. Having this common ground for measurements is important for providing a correspondence between maps and reality; so that, say, when a road is designed in a certain location, it can be built exactly where it was intended.
According to the engraved text, the penalty for disturbing this marker is a $250 fine or imprisonment. Considering it's embedded in a piece of concrete that's just sitting on the ground, I would guess that it has in fact been disturbed since its installation in 1932. Its NGS data sheet indicates that it hasn't been inspected since 1997; perhaps some construction in the last 15 years has displaced it.