The Crystal Mill, or the Old Mill is an 1892 wooden powerhouse located on an outcrop above the Crystal River in Crystal, Colorado, United States.
It is accessible from Marble Colorado via 4x4. Although called a mill, it is more correctly denoted as a compressor station, which used a water turbine to drive an air compressor.
The compressed air was then used to power other machinery or tools. Today it stands as a Colorado icon, and is reputed to be the most photographed site in the state.

In the 21st century, the mill is usually called the Crystal Mill or the Old Crystal Mill.
Many decades ago, when the mill was still in use,
it was called the Sheep Mountain Power House at the Lost Horse Millsite,
or simply the Lost Horse Mill. Sometimes it is erroneously called the Dead Horse Mill.

The mill was constructed in 1893 by George C. Eaton and B.S. Phillips, promoters of the Sheep Mountain Tunnel and Mining Company.
It was built as a power plant for the Sheep Mountain Tunnel.
Originally it had a horizontal waterwheel which generated compressed air for miners in the nearby silver mines.
It fell into disuse in 1917 when the Sheep Mountain Mine closed.
The mill was placed on the National Register of Historic Places on July 5, 1985.