The Strigfield Exclusion Zone is an area of 30km radius centered around the abandoned coal mining town of Strigfield. Located in the mountains of Tremenia and built on the site of a destroyed forest, the town and nearly all of its inhabitants were contaminated, killed, and reanimated by the sudden appearance of tangible chaos energy a few decades ago. Relief efforts proved disastrous, with many of the relief workers becoming contaminated as well, and in the end the town's fate became the centerpiece of a scandal with far-reaching consequences for the Navroyan Confederation, Tremenia, and the continent of Acetate as a whole.
Background
Strigfield was a mining settlement for Solcorp and operated much like other company towns on Acetate, with the entire town being built and owned by Solcorp and provided to the workers while they remained employed. The forest that was home to the now-extinct Strigafin was cleared to make way for the town because of extremely large deposits of anthracite coal underneath it, and the mines operated for several years before the first appearances of chaos energy.
The aftermath of the disaster included the implementation of a cordon to prevent civilians from entering the Zone, using a series of checkpoints along with border fences and walls and armed patrols along them. These guards were also in place in case anything inside the Zone tried to leave. This cordon would eventually become abandoned with the civil war in Tremenia escalating enough to make it a low priority to guard a wasteland.
A more detailed look at the events of the disaster and the Zone itself can be found in the documentary series Zone Patrol. (I'll get to it eventually, I swear.)