I'm not sure about all the key elements, but I assume the location Mesilla in New Mexico is one. And of course, the double eagle which might be a symbol or an object. And then there are the ghostly elements which could include sightings of apparitions or strange noises.
Well, first of all, the geographical location of Mesilla, New Mexico is a crucial element as it grounds the story in a specific place. The double eagle, whether it is a physical object like a coin or a symbol, is at the heart of the story. It might be that this double eagle has some sort of hidden past or significance. Then, the ghostly aspects are important. These could range from the typical ghostly sightings like seeing a figure in old - fashioned clothing related to the double eagle's history, to more intangible things like a feeling of being watched or a sense of unease in certain areas related to the double eagle. There may also be a backstory about how the double eagle came to be associated with the ghostly happenings, which could involve events like a long - forgotten crime or a lost love.