"Zong Sapa" aka "Chamasong". Unidentified place in Nepal near Mustang - Solved!

 

My text says "Zong Sapa or as they call it in the book now Chamasong". I can't identify either name, and I don't know what the book is!

The first version COULD be the place commonly known in the west as Jomsom, as this name is said to be derived from Dzongsam, Tib.: རྫོང་སམ་, which is said to translate as "New Fort". Well the Dzong is OK, but I can’t see how "sam" can mean new. If it’s "sar", which would mean new, then why that pronunciation? This eqivalence of Dzongsam with New Fort is found in many places on the net, but it's not impossible that they are copying each other's mistake!

And as for Chamasong, I just don't find it anywhere.

User Tingszin on Dharmawheel has found that "old maps have Jomosom, but also Rdzong gsar, referring to the same place." So the  identification has good evidence!