Sandy River is from the playing of Marcus Martin of western North Carolina, originally recorded in 1946. There is a great collection of his tunes (including this one) from the University of North Carolina at Chapel Hill label called: When I Get My New House Done (Western North Carolina Fiddle Tunes And Songs).

Another great source of Martin's tunes is from the Field Recorders' Collective, FRC 502 - Marcus Martin: Recordings from the collection of Peter Hoover.

In the below video, Mike Bryant & Paul Brown play this tune on their 2018 Bryant and Brown album the key of the original, which is in cross A, with the high string tuned to C# instead of E (fiddle-AEAC#). This is also known as Calico tuning, just one of the alternate tunings that Martin frequently used . Martin is likely the source of the term, from the popularity of one  of his well known tunes, "Calico". 

We still have to figure out which Sandy River this month's tune is named for. There are a lot of Sandy/Little Sandy/Big Sandy Rivers  - including a Big Sandy in Tennessee/Kentucky and a Big Sandy in W. Virginia/Kentucky. But let's put that aside for now and enjoy the tune!