Well, one possible element could be a hidden or forgotten burial ground near the Carbon River. Disturbing this burial ground might awaken something evil. Another could be a strange and malevolent creature that lives in the river, preying on anyone who gets too close. Also, there might be an old, abandoned building near the river with a dark history, and those who enter it experience terrifying hallucinations or encounters.
Ghosts. Maybe the spirits of those who died in or near the Carbon River.
I don't actually know the specific 'Carbon River Horror Story'. It could be about something terrifying that happened near the Carbon River, like a spooky encounter in the woods along its banks, or a strange phenomenon that has haunted the area around it.
One possible element could be a haunted bridge over the Willamette River. People might say that if you cross it at midnight, you'll see a ghostly figure.
Ghosts could be a possible element. In 1928, superstition was still quite prevalent, and a horror story might involve the apparition of a vengeful spirit.
One possible starting point is in the atmosphere as carbon dioxide.
One possible element could be a creepy old mansion. It might be abandoned and full of dark corners where strange things happen.
The waiter himself could be a key element. He might have a past he doesn't remember, which is somehow related to the horror. For example, he could have been involved in a murder at the restaurant in a past life, and now the spirits are coming back to haunt him. Also, the customers could be strange, like they are not really human but some sort of otherworldly beings just pretending to be normal diners.
One possible element is the sudden and terrifying hallucinations. People on bad 'ecstasy' might see grotesque monsters or distorted versions of people around them.
Malfunction could be one. Like when it doesn't stop vibrating or changes its pattern unexpectedly.
The Detroit Horror Story may contain elements such as the isolation of certain neighborhoods. These areas, cut off from the rest of the city, can feel like a world of their own, full of mystery and danger. The presence of graffiti - covered walls and broken streetlights can add to the spooky atmosphere. There could also be elements related to the city's history of racial tensions, which could manifest in stories of hauntings or vengeful spirits.