Alright, thinking about the environment of Upper Groam, it's a high valley between two mountain ranges, descending from a somewhat lower ridge down to the flatlands. I am imagining the area was built up over the eons by dirt blown up from western winds, so it's sandy soil and relatively arid, but not desert. Seasonal rains create rivers that may be dry part of the year, but they cut deep furrows in the relatively loose soil. The rivers are typically muddy and slow moving, and they are prone to changing their courses.
The rivers carry a great deal of silt, making their banks fertile and attractive to farming. The largest are navigable most of the year, but for the most part, the denizens of Upper Groam do not rely on them for trade and transportation.
Prior to the silver rush, Upper Groam was sparsely settled, but as mines sprouted to the north and south, many larger towns grew up along important routes from the mountains to the lowlands. Ascension was founded at the confluence of one of the region's only large rivers and a smaller seasonal tributary. The river is navigable during much of the year, so many silver and tin merchants set up shop to purchase metals from mining convoys and then send it the rest of the way to the lowlands by flatboat. Supplies flowed the other direction--up the river and into the convoys' carts and wagons.
When plague began striking the miners, the flow of silver and tin ebbed, and most of the wealthy merchants went with it. They were replaced by refugees from the mines and the crumbling cities of the Tawaren Basin. The influx of diseased outlanders prompted the Silver Watch to quarantine the town early. The first of the great walls was built on the western edge of Ascension, along with a quarantine jail used in an effort to prevent the illness from spreading further. The effort failed, and the line of quarantine was moved further westward, leaving Ascension fully in the grip of despair and death.