Ben,
I am attaching a screen shot of Salter's as it runs toward Atsion Lake. It can be viewed clearly and a lot of it can be walked starting at the northernmost bridge on Burnt House Road. (Locally Three Bridge Road)
The Mechescatauxin starts at Beaver Dam Lake in Waterford. It is usually mapped as the Sleeper after it leaves the lake. Salter's Ditch can be also be viewed easily from the old Raritan railbed just north of my pushpin. The road blew out a long time ago but there is a hidden footbridge nearby.
Scott