You are a US citizen and: 1  You are a first time applicant age 18 or older. 2  OR your most recent U.S. Passport was issued when you were under age 16. 3  OR your previous U.S. passport was issued more than 15 years ago.
Cave formations are called speleothem, from the Greek word spelaion, cave and thema meaning deposit. Almost all of them are made of calcite, the crystal of calcium carbonate. Different minerals and different movements in the water account for an incredible variety of cave formations.
Cave / Karst Systems. Hidden within the Grand Canyon are an estimated 1,000 caves. Of those, 335 have been recorded. Very few have been mapped or inventoried. Most have developed in the limestone of the Redwall and Muav formations, although some are known to exist in other formations. Some caves are well known and, over the years, have been frequented often by visitors, such as the Cave of the Domes on Horseshoe Mesa.