Randy Kennedy tells the story of the National Geographic Archives in the New York Times:

For many years there has been a kind of secret museum of photography under the streets of northwest Washington — an immense, windowless, climate-controlled archive with roots reaching back more than a century. […] The pictures make up the archive of the National Geographic Society, and it was this sentiment, said Mr. Bonner, the society’s archivist, that motivated him and officials there to explore the idea of opening up the holdings to the fine-art market for the first time. National Geographic’s goal is to find private and institutional collectors for the vintage black-and-white prints and later color images. […] After considering proposals from several dealers, the society recently chose the Steven Kasher Gallery in Chelsea, which has worked with several other large archives of photojournalistic images. On Sept. 17 the gallery will open its first exhibition of National Geographic pictures — 150 vintage prints from a dozen photographers. […] “Very little of this material exists anywhere else, because many of these pictures were taken specifically for National Geographic and they have the only copies,” said Mr. Kasher, who has previously overseen sales of images from the archives of The New York Times, The Daily News in New York and Magnum, the photo agency. Though prices for the prints have not been definitively set, they will probably range from $3,000 to more than $10,000 each, he said.

Treasures from an Underground Trove (New York Times)