Calona-Severing

In the year 70 AD, a great fault-shift in the northern Goatsback Mountains caused a large landslide to topple over a 150-foot-long ravine bridge that was Calona's only rail connection to the rest of the region. Having only a single rail connection is not unusual for citadels, but as Calona was nestled much deeper into the mountains than most other dwarven citadels, the engineering efforts to maintain the rail connection were more involved and dangerous than the others'. With Calona weathering heavy assaults from the Ironwrought Crusade for the past few years, maintainence on the bridge and other parts of the mountain track fell to the wayside. With the right natural push from what seemed an act of nature, the bridge suddenly gave way and tumbled down. It wasn't until no train had returned for a couple weeks that a brave adventuring party scouted down the tracks and discovered the bridge collapsed, along with the remains of 5 cargo trains.
Trains slowly stopped going to Calona from the outside world; beyond the first few months, only the occasional scouting train or especially brave conductors would try reaching Calona. In 72 AD, a train was traveling slowly enough due to prior engine damage that it saw the bridge was destroyed and managed to stop in time. It returned to Acarletto with the news that Calona had been permantly severed from the rail network, and no trains have tried going back since. Whether Calona has survived on its own is unknown to the rest of the world.
As long as the Ironwrought Crusade continues to be active in the area, Calona has been unable to replace the bridge. An attempt in 82 AD sent a large convoy of a thousand engineers, soldiers, and "volunteers" to the ravine to put together a replacement, but they only survived outside the citadel for a month. All they accomplished was a basic scaffold over the ravine, far from being able to support the weight of a train, and only 208 survivors made it back to the citadel after a deadly nighttime raid by the Ironwrought Crusade. No further attempts have been successfully organized, and Calona is severed from the rest of the world to this day.

Manifestation

The Calona-Severing was an especially violent example of a mountain fault-shift. A mountain cracked all the way up to the peak, and part of the mountainside fell away in a torrential avalanche, slamming into the bridge and causing its collapse. The crack was so loud that it echoed dozens of miles all the way to Calona, and is believed to be the loudest fault-shift ever heard from Calona.

Preliminary investigations in 73 AD by an adventurer-escorted engineering band noticed unusual blast marks and deep gouges in the metal, which are believed to have contributed to the weakening of the bridge prior to the fault-shift. The radiant metal in the bridge structure (an early and costly renovation in the early years after the world died) should have protected the bridge from sabotage from the Ironwrought Crusade and other undead, so it is unknown how, when, or by whom the damage could have gotten there.