Miners didn’t realize that the blue pebbles in the Yogo Gulch streams were sapphires for 16 years!

People had been mining the Yogo Gulch for gold for years before people realized there were highly valuable and high quality sapphires in the streams. Mining in the area had been popular, faded, and then become more common again in the area. For years, miners had noticed the blue pebbles in the stream, but never recognized them as precious stones. It wasn’t until 1895 when the sapphires were recognized for what they were officially. 

Jake Hoover thought the blue stones might actually be jewels and so he sent them to be looked at. Eventually, they were sent in a cigar box by uninsured mail to Tiffany’s in New York. Dr. George Frederick Kunz examined them and responded saying that they were in fact sapphires, and not only that, they were sapphires of very high quality! There are also some stories of other locals figuring out about the sapphires, though not officially as Hoover did. 

According to one story, a miner sent some gold and blue pebbles to a school teacher in Maine who recognized them as sapphires. There is also another story crediting S.S. Hobbs as recognizing the precious stones. 

(Source)