A large cache of Gold coins in a hollow under a broad, flat rock inside an Oak grove near their camp. Also, the mine itself, which was reported to be very rich, and the source of their income.
Two hard-luck miners who had unsuccessfully worked their way from El Paso, Texas, to the Nacimiento mountains of New Mexico finally struck a very rich gold vein high up in the San Pedro Peaks area. The older miner was holding out on the younger, secretly caching a large part of their shared profits. Incensed upon this discovery, the younger later struck the older one dead while double-jack mining and spent the following years fleeing his shame, which he tried to cover up as an Indian attack. Years later, when looking for the mine, he found out that an innnocent sheepherder had hanged for his crime, prompting him to hand a written confession to a priest in Bernallilo, NM before riding off into history a final time.
The overall area is public land. The mountains are very rugged on the West face, where many historians and local place the mine. Some of the area is Wilderness. The few dirt roads that climb the West side of the mountains are in bad repair. Access may be best from the San Gregorio Lakes area, where there are many camping spots and a trail head leading into the search area from the East.
The miners were supposed to have exchanged their Gold for goods and currency down in Lagunitas, NM, which is near Cuba, NM, so trails from there back into the mountains may be a good idea to search out. The miners worked at Copper City, which was just outside Cuba, north/north-west of the big open-pit copper mine.