Many markers are still metal. Wooden stakes may be used for temporary markings, but the actual reference points those are based on will be designed to be permanent.

You can probably find a variety of survey markers in the pavement in your neighborhood, if you know what to look for. For minor locations, they're usually a small pin driven into the concrete or asphalt.

For more major stations, they'll have a circular disk with information about the station. Even more rarely, you'll find geodetic survey markers that contain information about the actual curvature of the Earth at that point, since even the shape of the Earth can vary enough to be significant at large scales.

https://en.wikipedia.org/wiki/Survey_marker