Yule Marble is a marble of metamorphosed limestone found only in the Yule Creek Valley, in the West Elk Mountains of Colorado, 2.8 miles (4.5 km) southeast of the town of Marble, Colorado. First discovered in 1873, it is quarried today inside a mountain at 9,300 feet (2,800 m) above sea level, in contrast to most marble, which is quarried from an open pit and at much lower elevations.The localized geology created a marble that is 99.5% pure calcite, with a grain structure that gives a smooth texture, a homogeneous look, and a luminous surface. It is these qualities for which it was selected to clad the exterior of the Lincoln Memorial and a variety of buildings throughout the country, in spite of being more expensive than other marbles. The size of the deposits enables large blocks to be quarried, which is why the marble for the Tomb of the Unknowns, with its 56-long-ton (57 t) die block, was quarried from Yule Marble.Yule's quality comes at a high price due to the cost of quarrying in a high-altitude mountain environment. This challenge has caused the industry and the town of Marble to undergo many boom-and-bust periods since quarrying started in the mid-1880s, making the town emblematic of the economic fluctuations that beset a single-industry economy. Technology advancements in quarrying machinery and transportation have reduced, but not solved, the cost problem that afflicts the operation through the present.