-The Mandans: a study of their culture, archaeology and language, Volume 3 By George Francis Will, Herbert Joseph Spinden, page 140
"The Mandans (people of the pheasants) were the first people created in the world2, and they originally lived inside of the earth; they raised many vines, and one of them had grown up through a hole in the earth overhead, and one of their young men climbed up it until he came out on top of the ground, on the bank of the river, where the Mandan village stands. He looked around, and admired the beautiful country and prairies about him—saw many buffaloes—killed one with his bow and arrows, and found that its meat was good to eat. He returned and related what he had seen, when a number of others went up the vine with him. and witnesseth the same things. Amongst those who went up, were two very pretty young women, who were favorites with the chiefs, because they were virgins, and amongst those who were trying to get up, was a very large and fat woman, who was ordered by the chiefs not to go up, but whose curiosity led her to try it as soon as she got a secret opportunity, when there was no one present. When she got part of the way up, the vine broke under the great weight of her body and let her down. She was very much hurt by the fall, but did not die. The Mandans were very sorry about this, and she was disgraced for being the cause of a very great calamity, which she had brought upon them, and which could never be averted, for no more could ever ascend, nor could those descend who had got up;. but they build the Mandan village, where it formerly stood, a great ways below on the river; and the remainder of the people live under ground to this day.'" -
-< -->South Dakota historical collections, Volume 4 By South Dakota State Historical Society, South Dakota. Dept. of History, page 521
"The Numangkake [aka Mandan] now resolved to go up. The great chief with his medicine and his schischikue in his hand, went first. They climbed up, one after another by the aid of a branch of a vine; and when exactly half their number had ascended, and a corpulent woman was half way up the vine, it broke, and the remainder of the nation fell to the ground. This happened in the neighborhood of the sea shore. Those who had reached the surface went on till they came to the Missouri, which they reached at White Earth river. They then proceeded up the Missouri to Moreau's river. At that time they knew nothing of enemies. Once, when a Mandan woman was scraping a hide, a Cheyenne Indian came and killed her. The Mandans followed the traces of this new enemy till they came to a certain river, where they all turned back with the exception of two, the husband and the brother of the woman who was killed. These two men went on till they discovered the enemy, killed one of them and took his scalp with them. Before they got back to their village they found some white clay which they had never seen before, and took a portion of it with them. When they came to their great chief, the first man who had climbed up the vine, and whose skull and schischikue they still preserve, as a relic, in the medicine bag of the nation, they gave him the white clay, with which he marked some lines on his schischikue. The name of this chief was, at first, Mihti-Pihka (the smoke of the village), but when he ascended to the surface of the earth he called himself the Mihti-Shi (the robe with the beautiful hair). When he had received the clay and the scalp, he commanded all his people to shoot buffalos, but only bulls, and to make shields of the thickest part of the hide, which they did. When this was done, they asked the chief what were his next commandments. To which he replied, 'Paint a drooping sunflower on this shield' (as a sort of medicine or amulet), on which the sister of the chief said, 'You are fools; paint a bean on it; for what is smoother than a bean to ward off the arrows.'
"The chief now introduced the establishment of the bands or unions, and founded first that of 'the foolish dogs.' He made four caps of crows' feathers, and commissioned the Mandans to make a number of similar ones. He then gave them the war pipe and song, and exhorted them to be always valiant and cheerful, and never to retreat before the point of the arrow. He also gave them the strips of red cloth which hang down behind, and added that, if they would follow his directions, they would always be esteemed as brave and worthy men. The chief then made two of the bent sticks covered with otter skins, and gave them the kanakara-kachka. and then two others adorned with raven's feathers^ which he also presented to them. The first represent the sunflower, and the latter the maize. 'These badges,' said he, 'you are to carry before you when you go against the enemy; plant them in the ground, and fight to the last man, that is to say, never abandon them.' He next founded the band of 'the little foolish dogs,' and assembled many young men. whom he ordered to paint their faces of a black color, and gave them a song of their own, with the war whoop at the end. and said he would call them the 'black-birds.' He afterwards went to war with his people against the Cheyennes. They reached the enemy and laid all their robes in a heap together. The chief wore a cap of lynx skin, and had his medicine pipe on his arm. He did not join in the action, but sat apart on the ground during the whole time that it lasted. They fought almost the whole day, drove the enemy into their village, and were then repulsed, which happened three or four times, and one of the Numangkake was killed. When the chief was informed of this, he ordered them to go to the river and bring a young poplar with large leaves, which he planted in the ground near to the enemy, and challenged the Cheyennes to attack him; but they answered, they would wait for his attack. As he would not commence the combat, the enemy shot at him, but their arrows only grazed his arm and robe. He then held up the poplar, which suddenly shot up to a colossal size, was thrown, by a violent storm which arose, among the enemies, crushed many of them, and obliged the Cheyennes to retreat across the Missouri."
-South Dakota historical collections, Volume 4 By South Dakota State Historical Society, South Dakota. Dept. of History, page 569
2. Created chronologically first, but not as ancestors to all mankind. Other people came to be via separate, special creations. Quote: "The cattle were sent back to the east, where Lone Man also created white people. Lone Man created more humans, who grew and flourished. The first people he created were the Mandan." - link.
This is the Mandan nation's story of how they came from their subterranean world beneath the Earth via a vine (ala Jack and the Beanstalk) where they had lived for a very long period of time. It is their origin on the surface and the start of their history along the Missouri River. They have had this national tradition told orally for their entire known history. Further, along with their momentous origins, they get into quick conflict with the Cheyennes - who they manage to defeat by way of a miraculous poplar - another national tradition.
As Rabbi Gottlieb says, "Any national miracle that would create a national tradition is unforgettable. So, if a nation believes in such a miracle, we have sufficient reason to accept that belief as true." -link
Or do we?