Along some long dried-up fork in a long dried-up river in Nubia (modern Sudan) was a semi-arid river valley. It was brimming with stone and semi-precious metals (like iron). And while the banks of the river were hardly the greenest in the world, some farming could certainly be done. However, no farming had ever been done because it was completely unsettled. Not a trace of civilization was to be found in the region - not even so much as a potsherd.
That is, until one Mamluk merchant got lost trying to take a shortcut from Aswan to Nuri, and ended up finding this very valley. His navigator mapped the area, knowing it would be of value to some Arab or Crusader explorer. And it was - to you.
What will you make of the sheer cliffs on either side? The semi-fertile farmland which is across the river from rich stone and iron deposits? The Nubian, Egyptian, and Crusader forces that know about your fascinating find and will invade you from all sides?
It's completely up to you in the self-proclaimed LIME RIVER VALLEY!
(Either that, or this is a fictional town builder in the Southwestern United States full of Indians, Spaniards, and... I dunno. Ottomans. You pick.)