Mariposa County Sheriff's Deputies said the robbery was reported around 4 p.m. but officials were not able to locate the suspects described by witnesses after arriving on the scene.
Authorities now estimate robbers stole about $2 million worth of minerals from a Mariposa museum.
The Mining and Mineral Museum contains examples of rare and valuable minerals from around California and the world, including gold. Parts of the collection date back more than a century.
