Image source: http://russbishop.photoshelter.com/image/I0000O12sX0mq9bU

Material: Limestone

Process: Tufa is a type of limestone that is formed when calcium-rich spring water mixes with the carbonate-rich Mono Lake water and precipitates around the spring. The towers grow underneath the waters surface. Sand Tufa is formed in more sandy regions of the lake near the shore. When the lake level dropped these tufa were exposed to the elements, the wind blew away the remaining sand, leaving these unique formations behind.

This is interesting because it has been under the water and can only be seen now because of environmental changes. The shapes are very interesting and complex.