The site is supposed to be somewhere around Hot Springs Arkansas, in the National forest. I found a link to the story, as told by the Manataka American Indian Council, a page on their website.
http://www.manataka.org/page2.html
It shows the scope of importance for this historical site. Might just add a couple quotes here...
"For thousands of years, this magnificent site was the gathering place of many nations. Tribal leaders and spiritual elders made pilgrimages to the Great Ma-na-ta-ka Mountain to sit in great councils with many tribes. Some came every seven years, others came every eleven years, and others made the journey more frequently depending on local custom."
"Ancient tribes came to Manataka on pilgrimages to place ceremonial items in five of the caves. The people of the south laid gifts in the southern-most cave and people of the north laid their gifts in the northern-most cave. Two other caves were used by the people from the west and east for offering ceremonies. The cave located to the left of the crystal cave was used by the 'Keepers of Manataka', the Tula Indians of Tanico, who lived in surrounding areas and for other tribes living nearby such as the Caddo, Quapaw, Osage, Tunica, and Pawnee. To the right of the center crystal cave was a ceremonial cave reserved for gifts of the other people of this land"
"The Lady of the Rainbow, referred to as Ix Chel by the Maya, was said to have presided over the peace in the valley. Dressed in all white buckskin and holding one eagle feather in each hand, she stood on the mountain overseeing the peace."
"Manataka is truly the place of peace for all people. The area was a cultural and trade center for all native peoples – a great melting pot of American Indian culture. The Valley of the Vapors was neutral territory unclaimed by any tribe."
"Settlers and the U.S. government destroyed the sacred Circle and the seven ceremonial caves containing the Manataka Stone and other ancient artifacts gifted to Manataka by the tribes. Stolen artifacts were sold for profit by government agents. Government bureaucrats, to cover up gross negligence of the past, claim there were never any caves on the mountain, regardless of strong evidence to the contrary."
