Case file · Folklore / legend
The Coso artifact
On 13 February 1961 rock hunters near Olancha cut open what they took for a geode and found a metal core in ceramic. Promoters called it a 500,000-year-old machine.
1961 CE · 36.29, -117.99 · status: explained
The account
It became a staple of 'out-of-place artefact' books.
The sceptical view
In 1999 spark-plug collectors identified it from X-rays as a 1920s Champion spark plug encased in iron-rich concretion.