The station site and the Pony Express Monument are in separate locations.
The site is at https://goo.gl/maps/6ecT5eFvKsvLdtXM9. In satellite view, it appears there is a cutoff from the XP Trail just before the trail turns south to Thompson Ranch (at the west end of Telegraph canyon).
According to the US Topo map, the monument is located by the Thompson Ranch approximately at the POI water icon. (“There is a brass Pony Express centennial plaque mounted in a stone and concrete monument near the ranch house just one mile south of the actual station site.”)
One author (Hill, p.222) states (without citation) that Diamond Springs served as a gathering place during the Pauite War.