In Game Description via Character Origins in Character Creation:
"Beneath the mysterious Star Mounts, at the southern edge of the ancient High Forest, the Gray Vale straddles the river Delimbiyr in the North. The dangerous wilderness helps produce a hardy breed of adventurer."
The Gray Vale is so known because of the River Grayflow, a tributary of the Delimbiyr River, which is considered the main watercourse of the region - flowing all the way to the Sword Coast, and the Graypeak Mountains to the east. The lands were once known known as the Delimiyr Crescent and Grayvale was but a part of that area but since the Spellplague eradicated most of the smaller settlements in the area, the nomenclature was simplified.
The Grey Vale is known for its fertile farmlands and the boats that travel up and down the Delimbiyr river, providing trade to all of the settlements along its banks. Particularly aggressive goblins, the bandit kingdom of Llorkh and frequent raids by bugbears breed a tough but also a cosmopolitan people. The area was populated exclusively by elves for at least a millenium and a few still decide to come here from the High Forest. Half-elves are the descendants of those folk, only slightly outnumbered by humans, whom they resemble more than most half-elves do due to the long-time intermarriages with human settlers. Dwarves searching for the ancient legacies of their people also populate the area.
The primary settlement in the Gray Vale is Loudwater. Though not as large or as beautiful as it once was, its walls keep the residents safe from outside threats and it is by far the largest bastion of civilization for many miles.
The magical Dire Wood and nearby White Fate beholder hive provide ample tests for experienced adventurers. Rumours are also rife about serpentfolk infiltrators from Najara and abandoned dwarf holds, still unlooted, in the Graypeaks.