While in a human-centric fashion, it is convenient to speak of the Valley in Political terms by referencing the Westron Baronies, there are other considerations.
When talking about the geography of the valley, or the non-human Flora and Fauna, it is perhaps better to speak of the Northern and Southern regions of the valley.
In brief, these are defined by the Nine rivers, in terms of separation one from another, and the big divide between North and South is of course the Great River. What follows is a brief naming and description of the regions, Northern first, from west to east.
The most western of regions north of the Great River is mostly plains. It is bounded on the north by the western reaches of the Destriel Mountains. The eastern edge of the shattered plains run up against the Durwash River. The southern boundary is the Great River, and to the west is the defacto edge of the Valley of the Old Ones. The western edge of the valley is patrolled by great hosts of the Omart Empire.
As the empire is certainly not interested in entering the Valley (or involving itself with the Westron culture that has taken root here), and the large military patrols seem charged with keeping all FROM the valley contained IN the valley - there have been few large expeditions west.
Geographically, the shattered plains are quite interesting. They were once overrun by large icefields and glaciers from north of the Destriel mountains, and when the ice receded, the region was strewn with many bolders and singular rocky formations jutting up out of the plains.
The only Westron Barony to call the shattered plains home is the Granite Hold at Hogle, capitol of the Barony of Hogle. Although Hogle is the oldest of the baronies (first settled in the year 26, some 1500 years ago), it is also one of the smallest. It boasts a size of only 18,000 in the capitol city. The city is home to the Knights of Torisch, and their curious allies the Aublan Cat Riders. The Cat Riders, of course, ride the great plains cats that live in the region. Like much of the rest of the northern regions, the animals here have adapted to the sweeping cold that comes down out of the Destriel, and includes giant elk, great wooly mammoths and rhinos, and the great wooly buffalo. Only here, however, are the great plains cats found.
The Aublan valley is home to the Cat Rider peoples (who are semi-nomadic, moving north to Aublan for the summer and the breeding season, but moving south to near the Great River for winter). Aublan riders, who are quite proficient with the small horned bows that they shoot from atop their giant riding cats, are allied with the Barony of Hogle (or more accurately, with the Grand Master of the Knights of Torisch). The Aublan riders are divided into two "nations" or collectives of clans,the Northern Hunt, and the Southern Pack.
Together they protect the region from maruding orcs and hobgoblins out of the mountains; from rampaging raids of Storm King Tribe barbarians; from the overzealous encroachments of Omart Empire patrols, and finally from the occasional uprisings of the primitive Keepi-keepi people who live among the great stones of the plains.