Geologists in 1875 commonly believed silver was not found in sandstone, yet the Silver Reef area contained the only known occurrence of commercially mineable silver ore in sandstone in the United States. More than $10 million worth was mined and milled during Silver Reef's boom years from 1875 to 1888. In 1866, prospector John Kemple discovered high-grade loose silver known as float near Harrisburg at the southern end of White Reef, and the search for its source led to the discovery of a few deposits in sandstone reefs north and west of Leeds in 1868. Widespread disbelief that silver could occur in sandstone kept many prospectors away for eight more years, but by early 1876 enough claims had been made to spark broad interest and draw prospectors and miners to the new town of Silver Reef. Twelve years later the ore had largely played out, the boom had ended, and reduced operations continued through 1909, after which mining essentially ceased. The district's reefs were created when rock layers in southwestern Utah were buckled and then raised and lowered by faulting, producing upturned edges resembling reefs in the ocean. Four such reefs are in the Silver Reef mining district; White Reef is the longest, but Buckeye Reef produced most of the silver mined there. The silver occurred in the Springdale Sandstone Member of the Moenave Formation, an early Jurassic sandstone nearly 200 million years old, and geologists have proposed volcanic, sedimentary, and ground water origins for how it came to be deposited there.