Most people dig through mines looking for precious stones or minerals. Michael Allen Harris hunts for jeans.

The commercial painter from Orange County originally scavenged the abandoned silver mines of California, Nevada, and Arizona for antique bottles. The glass fetched high prices from collectors—but not as high as the vintage denim that Harris found tucked beneath the earth, left behind by 19th-century workers.

Harris started collecting the old cloth, and he soon evolved into a self-described “denim detective.” Over the years, he’s amassed countless clothing items, including one of the oldest jean jackets in existence and a pair of pants dating back to 1873. Harris chronicled some of these findings in his 2010 book Jeans of the Old West, which includes both photos of his rare discoveries and a history of the region's love affair with the durable fabric.

The self-taught historian’s hobby isn’t just pleasurable—it’s also profitable. According to The Guardian, Harris once sold some jeans to a collector for $30,000, and he’s received offers as high as $100,000. Denim companies like Levi’s like to nab Harris’s finds for their archives so designers can study the wear patterns that give trousers that distinct, lived-in look.

Check out Harris's Flickr account to view his pictures of just-dug-up denim. 

[h/t The Guardian]