Gold coins with face value of $50,000 in the 1880’s.
Bandits seeking shelter at a hidden cabin happen across other bandits that are already there, countng their own loot. As the smoke clears, only one is left alive. He rides away, only able to carry a small portion of the gold coin loot, and is never able to find the place again.
Two men on the run seek shelter at a hidden cabin in the malpais (lava flow) in Valencia County on their way East, only to find it occupied by very nervous bandits that open fire on them immediately. After the smoke clears, only the fugitive Twadell is alive, and he is stunned by the $50,000 in neatly-stacked Gold coins he finds in the cabin. Already with $1,000 in his pocket and on the run, Twadell buries the coins in the cabin, and moves on quickly, expecting to return. Fourty years later, he finally makes it back, and enlists the aid of a local treasure hunter in his pursuit. Eventually finding the cabin that “surely” must be it, they excavate everywhere that they think makes sense, but to no avail.
The malpais in New Mexico shows up aross the state in a number of places where there has been recent volcanic lava flows. These areas are often large, and some are huge. In Valencia county, the search ares is extensive. Portions are in a National Monument, Indian Land, Private, or open-access such as BLM. The particular area of your search will dictate access, but the region is very remote, so travel with care.