Editing Mammoth Cave National Park (section)

===The longest cave (1954–1972)===
[[File:Mammoth Cave Mammoth Dome.jpg|thumb|upright|Staircase tower in Mammoth Dome]]

By 1954, Mammoth Cave National Park's land holdings encompassed all lands within its outer boundary with the exception of two privately held tracts. One of these, the old Lee Collins farm, had been sold to Harry Thomas of Horse Cave, Kentucky, whose grandson, William "Bill" Austin, operated Collins Crystal Cave as a show cave in direct competition with the national park, which was forced to maintain roads leading to the property.

In February 1954, a two-week expedition under the auspices of the [[National Speleological Society]] was organized at the invitation of Austin: this expedition became known as C-3, or the Collins Crystal Cave Expedition.<ref>Lawrence and Brucker 1955</ref>

The C-3 expedition drew public interest, first from a photo essay published by Robert Halmi in the July 1954 issue of ''True Magazine'' and later from the publication of a double first-person account of the expedition, ''The Caves Beyond: The Story of the Collins Crystal Cave Expedition'' by Joe Lawrence, Jr. (then president of the National Speleological Society) and [[Roger Brucker]]. The expedition proved conclusively that passages in Crystal Cave extended toward Mammoth Cave proper, at least exceeding the Crystal Cave property boundaries. However, this information was closely held by the explorers: it was feared that the National Park Service might forbid exploration were this known.<ref>Brucker and Watson 1976 p. 31</ref>

In 1955, Crystal Cave was connected by survey with Unknown Cave, the first connection in the Flint Ridge system.

Some of the participants in the C-3 expedition wished to continue their explorations past the conclusion of the C-3 Expedition, and organized as the Flint Ridge Reconnaissance under the guidance of Austin, Jim Dyer, John J. Lehrberger and E. Robert Pohl. This organization was incorporated in 1957 as the [[Cave Research Foundation]]. The organization sought to legitimize the cave explorers' activity through the support of original academic and scientific research. Notable scientists who studied Mammoth Cave during this period include [[Patty Jo Watson]] (see section on [[#Prehistory|prehistory]]).

In March 1961, the Crystal Cave property was sold to the National Park Service for $285,000.<ref>Bridwell 1952, p. 59.</ref> At the same time, the [[Great Onyx Cave]] property, the only other remaining private [[inholding]], was purchased for $365,000. The Cave Research Foundation was permitted to continue their exploration through a Memorandum of Understanding with the National Park Service.

Colossal Cave was connected by survey to Salts Cave in 1960 and in 1961 Colossal-Salts cave was similarly connected to Crystal-Unknown cave, creating a single cave system under much of Flint Ridge. By 1972, the Flint Ridge Cave System had been surveyed to a length of {{convert|86.5|mi}}, making it the longest cave in the world.