The thing that confuses us laymen is the term "based on." Grid north is calculated from coordinates and true north can then be calculated from grid north. Both are "based on" a grid but it's not at all clear to me which was used.
The grid bearing is based on grid coordinates, which are based on geodetic coordinates, which are referenced to the underlying geodetic datum.
If a projection is being used (not just an assumed Cartesian system) everything starts with the geodetic datum.
Unfortunately a lot of surveyors consider geodetic datum citations to be "elitist" or an indication of "button-pushing" or "mathemagical surveying" rather than a critical piece of information that allows subsequent retracement surveyors to follow in their footsteps more easily.
You're gonna have to show that to me. I've never seen any rotation between epochs.
While it's not common (seen it on the west coast & AK depending on location, size and date) it doesn't mean that the geodetic basis and the method of tying to it aren't critical information that helps the next surveyor.
The relative slopes and elevations on a topographic survey site may not change, but the base datum might, so we still reference it.
It is common practice in California to use CCS grid bearings with ground level distances. Grid distances will almost always be slightly shorter.
Don’t shoot the messenger.
Thank you all for your many enlightening remarks and reflections!
Yes, the map is in (or "based on") grid bearings and ground distances. The point at which gamma was taken is shown elsewhere on the map.