Why did Billy bury Old Dan on the top of the hillside in Where the Red Fern Grows?

Billy buries Old Dan on the top of the hillside because it is a beautiful place where the wild mountain flowers grow. Billy says,

"I had a purpose in burying my dog up there on the hillside. It was a beautiful spot. From there one could see the country for miles, the long white crooked line of the river, the tall thick timber of the bottoms, the sycamore, birch, and box elder. I though perhaps that on moonlight nights Old Dan would be able to hear the deep voices of the hounds as they rolled out of the river bottoms on the frosty air."

Billy had loved his dog beyond measure, and burying Old Dan at the most beautiful place he can think of affords him a bit of solace at his loss. When Little Ann dies shortly thereafter, Billy buries her there too, and marks the spot with a piece of sandstone on which he carves the dogs' names. The following spring, when the family moves away from the mountains and into town, Billy returns to the graves to say good-bye to his dogs. He is amazed to find that, between the two little mounds,

"a beautiful red fern had sprung up from the rich mountain soil...fully two feet tall...its long red leaves...reach(ing) out in rainbow arches curved over the graves of (his) dogs."

According to an old Indian legend,

"only an angel could plant the seeds of a red fern, and...they never died; where one grew, that spot was sacred."

Billy has chosen the spot for his dogs' graves well. As it turns out, he does not return to the Ozark Mountains and the land that he so loves, but in his heart he believes that the red fern has continued to grow, covering the graves of Old Dan and Little Ann, keeping their remains secret and safe beneath its long, red leaves (Chapters 19-20).