They are in limestone.
Acidic ground water (rain-water that has absorbed atmospheric carbon dioxide to form carbonic acid) dissolving the limestone as it flows through the joints & other discontinuities in the rock mass.
Gypsum is similarly soluble and can form caves in the right circumstances. So is dolomite but the structural nature of dolomite deposits prevents cavern development.
limestone
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Carbonic Acid
no
Sinkholes and caverns are formed from carbolic acid. This carbolic acid dissolves rock which creates the spaces that form the sinkholes and caverns. The carbolic acid is created when carbon dioxide dissolves in water.
limestone
It is one of the most famous.
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carlscad caverns
Most caverns form through a process called speleogenesis, which occurs when groundwater dissolves limestone or other soluble rocks over millions of years. These dissolved materials create openings and passages underground, eventually forming caverns. The most common locations for cavern formation are in areas with thick limestone deposits, such as karst regions.
The limestone caverns themselves are formed by groundwater gradually dissolving the limestone rock. In this process, some of the limestone is taken into solution, and under favourable conditions, it will form a drip on the roof of a cavern. This may eventually build to form a stalactite above, and perhaps also a stalagmite below it.
erosion and uplift
The great state of TENNESSEE
The three miles of permitted visitation of Carlsbad Caverns is one of the most accessible and most beautiful caverns in the world, having one of the largest (in terms of volume) underground rooms anywhere.
carlsbad caverns
Oceans push rocks underground to form caverns.
Carbonic Acid