A close reading of the narrative answers these questions. Here's the passage:
A single knoll rises out of the plain in Oklahoma, north and west of the Wichita Range. For my people, the Kiowas, it is an old landmark, and they gave it the name Rainy Mountain.
The Wichita Range is a mountain range located in southwestern Oklahoma. Momaday also explains why he returned:
I returned to Rainy Mountain in July. My grandmother had died in the spring, and I wanted to be at her grave.
Momaday's journey is a personal journey. He goes home out of love and respect for his grandmother. He wants to visit her grave, grieve her loss, and honor her memory. Also, by going home he returns to his own cultural roots and embraces his heritage.
In the book, Rainy Mountain is a small hill situated on the Oklahoma plains, north and west of the Wichita Range. The weather at Rainy Mountain is known to be extreme in all seasons. For example, winters bring substantial blizzards, springs herald the onslaught of tornadoes in the region, and summers unleash unbearable heat on all living things.
This is where the author's grandmother, Aho, used to live. The author returns to visit her grave. Since she is newly deceased, the author's grief is still fresh in his mind. He returns to reminisce about his grandmother's life and to remember the history of his people, the Kiowas.
The author relates that Aho was born when the Kiowas "were living the last great moments of their history." Almost a decade before she was born, a majority of Kiowa warriors were captured and imprisoned by the US Cavalry at the old stone corral at Fort Sill. There, the warriors were stripped of their horses and weapons. Nearly 800 ponies were killed, and an additional 2000 horses were either sold or given away. When she was seven, Aho experienced the last of her people's Sun Dance culture "when the last Kiowa Sun Dance was held in 1887 on the Washita River above Rainy Mountain Creek."
The central figure in any Sun Dance is always the Tai-me, the "sacred Sun Dance doll." In the book, the Tai-me is described as a small, green-stoned human figure less than two feet in length. The figure is elaborately dressed in a white-feathered robe; it also wears a headdress consisting of a single feather and pendants of ermine skin as well as strands of blue beads around its neck. The face, chest, and neck of the figurine is painted with symbols of the sun and moon. The Tai-me is always preserved in a rawhide box and only exposed during Sun Dances; it is considered a sacred relic. Momoday recalls that the Tai-me was brought out for the last time in 1887.
By this time, the buffaloes that the Kiowas had always depended on had already been annihilated. Often, the remaining members of the tribe had to kill and eat their own ponies to prevent themselves from starving to death.
So, Momaday returns to Rainy Mountain in order to reminisce about his grandmother's life, to contemplate the illustrious history of his own people, and to eventually memorialize in print the richness of his own heritage.