The Coso Artifact is a spark plug found encased in a lump of hard clay or rock on February 13, 1961 by Wallace Lane, Virginia Maxey, and Mike Mikesell while they were prospecting for geodes near the town of Olancha, California and long claimed as an example of an out-of-place artifact. Following its collection, Mikesell destroyed a diamond edged blade cutting through the rock containing the artifact and discovered the item. Within a three-paragraph letter,Virginia Maxey, one of the discoverers, wrote:
"In the opinion of one trained geologist, it has taken at least 500,000 years for this nodule to attain its present form—and yet, when we cut it open, we discovered a manmade object within the geode's cavity"
It is well documented that the nodule surrounding the spark plug may have accreted in a matter of years or decades as demonstrated by examples of very similar iron or steel artifact-bearing nodules.
On September 9, 1999, Chad Windham, President of the Spark Plug Collectors of America, identified the Coso Artifact as a 1920s-era Champion spark plug, which was widely used in the Ford Model T and Model A engines. Other members of the spark plug collector community soon concurred with this assessment.