Later influences on Greyhawk material in 2e and 3e gave names to lots of the specific regions that didn't have names on the original folio or box set editions - "Mistmarsh" was the name given, probably by Sargent or Moore, to the wetlands area around these rivers SE of Greyhawk. One of the things I loved about Greyhawk was that as a published setting it wasn't so specific and allowed us to find our own heroes and villains - I'll be honest I never heard the names Mordenkainen (sorry Gary

) till I was much older and so they weren't a part of my teenage Greyhawk campaigns.