Final answer:
Surveyors establish benchmark marks, also known as leveling marks, to determine the true elevation at a site.
Step-by-step explanation:
To locate the true elevation at a site, surveyors have established benchmark marks also known as leveling marks. These marks serve as reference points for determining the height or elevation of a specific location. Surveyors use various techniques and instruments, such as leveling instruments and GPS receivers, to measure and establish these benchmark marks.