What do you think Momaday means when he calls the Kiowa migration “a journey toward the dawn” in The Way to Rainy Mountain?
[Taken from a paragraph of the book]
"Her name was Aho, and she belonged to the last culture to evolve in North America. Her forebears came down from the high country in western Montana nearly three centuries ago. They were a mountain people, a mysterious tribe of hunters whose language has never been positively classified in any major group. In the late seventeenth century they began a long migration to the south and east. It was a journey toward the dawn, and it led to a golden age. Along the way the Kiowas were befriended by the Crows, who gave them the culture and religion of the Plains. They acquired horses, and their ancient nomadic spirit was suddenly free of the ground. They acquired Tai-me, the sacred Sun Dance doll, from that moment the object and symbol of their worship, and so shared in the divinity of the sun. Not least, they acquired the sense of destiny, therefore courage and pride. When they entered upon the southern Plains they had been transformed. No longer were they slaves to the simple necessity of survival; they were a lordly and dangerous society of fighters and thieves, hunters and priests of the sun. According to their origin myth, they entered the world through a hollow log. From one point of view, their migration was the fruit of an old prophecy, for indeed they emerged from a sunless world."
I think to answer your question you need to realise that the quote you gave is actually a metaphor. The key to working out what the author is talking about relates to the images that the word "dawn" creates in our mind. Consider the fate of Aho's tribe before their migration and note how they were described:
They were a mountain people, a mysterious tribe of hunters whose language has never been positively classified in any major group.
They were an indistinct tribal group without their own separate ethnic identity. However, their migration changed that as it triggered "a golden age" for this tribe. The migration, through the people they met and the change in location, gave the Kiowa people a new culture, which included a new religion and a sense of pride in their own tribal identity. So much so, that when they entered the southern Plains the texts tells us they had been transformed:
No longer were they slaves to the simple necessity of survival; they were a lordly and dangerous society of fighters and thieves, hunters and priests of the sun.
Thus we can understand why the metaphor is appropriate. It was a new, glorious start for the tribe, just as dawn signifies a new beginning for the world.