Case of the Cosa Artifact
While mineral hunting in the mountains of California near Olancha during the winter of 1961, Wallace Lane, Virginia Maxey and Mike Mikesell found a rock, among many others, that they thought was a geode - a good addition for their gem shop. Upon cutting it open, however, Mikesell found an object inside that seemed to be made of white porcelain. In the center was a shaft of shiny metal.
Experts estimated that, if this was a geode, it should have taken about 500,000 years for this fossil-encrusted nodule to form, yet the object inside was obviously of sophisticated human manufacture. Further investigation revealed that the porcelain was surround by a hexagonal casing, and an x-ray revealed a tiny spring at one end, like a spark plug. There's a bit of controversy around this artifact, as you can imagine. Some contend that the artifact was not inside a geode at all, but encased in hardened clay.
The artifact itself has been identified by experts as a 1920s-era Champion spark plug. Champion Spark Plugs is a company that is still active today: ChampionSparkPlugs.com.
Unfortunately, the Coso Artifact has gone missing and cannot be thoroughly examined. Is there a natural explanation for it? Or was it found, as the discoverer claimed, inside a geode? If so, how could a 1920's sparkplug get inside a 500,000-year-old rock?
A Time/Space Anomaly
Could a naturally occuring time/space anomaly have sucked the spark plug back in time?
A Time Travel Experiment
Could the US government or a private individual/group have created a time travel device? The device may have used the spark plug for some reason in it's design. Perhaps the early Champion Spark Plug company had links with military research facilities or maybe their spark plug was used merely because it was a readily available part.
This external link contains detailed information about the mystery: