Just finished reading
Climax: The History of Colorado's Climax Molybdenum Mine--Mountain Press Pub Co. (Paperback)
~ Stephen M. Voynick
Stephen M. Voynick (Author)
ISBN-10: 0878423540
ISBN-13: 978-0878423545
http://www.amazon.com/Climax-History...2660051&sr=1-1
It is about a molybdenum mine in Colorado. If you have interest in mining or construction, it is a great read and your municipal library may have it available for loan. The mine was one of the first, if not the first to use a block caving technique to carve out a cave inside, then blow the roof and have the mountain collapse on itself causing a glory hole depression seen from the surface.
warning - as a side note, do not search for "climax glory hole pictures" from work. The term has alternate meanings.