The Marideth River valley is a region of Nirmathas that roughly encompasses the southeastern portion of the country, primarily south of the Marideth River. The Molthuni city of Fort Ramgate is also considered part of the river valley.
This region has been a primary battleground in the decades-long war between Nirmathas and Molthune. As such, only a couple of small human villages exist here: Acorn's Rest and Purt. Fangwood Keep and Raven's Beak are former military strongholds that have either been abandoned or ruined during the war. Haunted or tainted locations within the area include the Dark Grove and Deadeye's Haunt.
Non-humans have also made this region home. A tribe of centaurs lives at Seesaw Rock, hobgoblins infest a cave network on the western edge of the region, and a troll has taken residence in a nearby cave. Numerous fey claim fiefdoms along the river banks, though frequent flooding redraws the borders with regularity. A sea hag named Schemedzah, an exile from Lake Encarthan, has been uniting the fey under an iron fist to retake her territory at the lake.