Crystal Grottoes

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Coordinates: 39°29′53″N 77°40′37″W / 39.498°N 77.677°W / 39.498; -77.677

Formations on the ceiling of one of the Grotto passageways

Crystal Grottoes is the only show cave in the U.S. state of Maryland. It is located on Maryland Route 34 between Boonsboro and Antietam National Battlefield.


Crystal Grottoes was discovered in 1920 in the course of quarrying operations by a road construction crew trying to obtain gravel.[1] A drill bit (for placing explosives) disappeared into a hole, and the crew realized they had found a cave. Blasting produced the entrance which is still used, and in 1922 the cave was opened to the public. A mapping operation in 1968 revealed about a half mile of passages, but only about one third of the cave is accessed during the tour, which takes about forty minutes.

A fire in December 2007 caused substantial damage to the visitors center.


Cascade Formations in the Fairy Land Area showing off their blue tint

Crystal Grottoes is an example of a karst cave, formed in an anticline in a bed of Tomstown Dolomite. The cave is essentially horizontal throughout its extent and the passages are typically high and narrow. A great deal of brown and red clay fills most of the cave to a considerable extent; the commercial tour routes involved the removal of up to 6 feet (1.8 m) of this clay in places. Sediment fills many of the undeveloped passages to within a foot or two of the ceiling, thereby making many crawlways. No streams exist in the cave, although a small "lake" or pool is maintained by drip water.

Most of the rooms abound in formations, generally stalactites, flowstone, and columns. They are typically white or buff, with one area (called Fairyland) tinted a light blue, perhaps by copper oxides.

The first room is 8 feet (2.4 m) below the entrance house and is oblate in shape, being 30 feet (9.1 m) long, 10 feet (3.0 m) wide, and 15 feet (4.6 m) high. At each end it is pinched out by mud flows and narrowing of the passage. This room originally contained a considerable number of formations, but quarrying operations and clearing of passages have removed them except along the west wall where flowstone and stalactites are abundant.

The building at the entrance to Crystal Grottoes

With the exception of the passage from the Blanket Room to the exit, the passages are continuously lined or covered by formations. Delicate drape-like stalactites, bacon rinds, and stout columns predominate. The colors are generally pure white or buff with occasional deeper tints. The passages forming Fairyland are studded with stalactites and stalagmites of a delicate light blue hue.

The Blanket Room is the largest room in the caverns at 30 feet (9.1 m) and 20 feet (6.1 m) wide. Large sheets of stalactites and bacon rind hang in clusters from the ceiling, which is here 20 feet (6.1 m) high.

The passage leading to the Golden Lake is profuse with formations and in part is bridged by flat-lying travertine, a condition that is found in many of the passages not open to the public. The Golden Lake is a small pool fed by water dripping from the ceiling. In wet seasons the water accumulates at a rate necessitating periodic bailing.

The passages not open to the public are similar to those already described except they are constricted at many points. Orange-brown clay that covers the floor and lower walls of these passages is often overlain by calcareous formations. The commercial tour route covers approximately one third of the known cave.[2]

Unlike many show caves, the electric lighting at Crystal Grottoes is uncolored, allowing the visitor to see the formations' natural appearance.


  1. ^ Crystal Grottoes web site
  2. ^ Maryland Geological Survey

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