There is a very important quotation that Momaday shares with us at the very beginning of The Way to Rainy Mountain that can help you understand why this real mountain is important to the Kiowa culture:
[While looking at Rainy Mountain] our imagination comes to life, and this, you think, is where Creation was begun.
This statement alone inspires the beautiful imagery of this mountain which has become an important Kiowa landmark. Why? The Kiowa tribe has always placed great importance on the Sun through their religion of worshiping Tai-me and the Talyi-da-i bundles. It is here, at the foot of Rainy Mountain, where the Kiowa would dance the Sun Dance, which became very sacred to the people. It was, in fact, the only day that the effigy of Tai-me (an interesting half-bird and half-mammal statue) was both revealed and worshiped. Momaday especially reminds us of the very last complete Sun Dance that was, again, danced at the foot of Rainy Mountain at the Rainy Mountain Creek of the Washita River. This was the last time the Sun Dance was done in its entirety. Momaday's grandmother was lucky enough to attend that last, complete ceremony. The following time, in 1890, the soldiers at Fort Sill showed up and dispersed the Kiowa tribe before the ceremony was complete.