This text comes direction from History of the Church – Joseph Smith Volume 2 pages 79-80 copyrighted by George Albert Smith for the Church of Jesus Christ of Latter-day Saints.
During our travels we visited several of the mounds which had been thrown up by the ancient inhabitants of this country – Nephites, Lamanites, etc., and this morning I went up on a high mound, near the river, accompanied by the brethren. From this mound we could overlook the tops of the trees and view the prairie on each side of the river as far as our vision could extend, and the scenery was truly delightful. On the top of the mound were stones which presented the appearance of three altars having been erected one above the other, according to the ancient order; and the remains of bones were strewn over the surface of the ground. The brethren procured a shovel and a hoe, and removing the earth to the depth of about one foot, discovered the skeleton of a man, almost entire, and between his ribs the stone point of a Lamanitish arrow, which evidently produced his death. Elder Burr Riggs retained the arrow. The contemplation of the scenery around us produced peculiar sensations in our bosoms; and subsequently the visions of the past being opened to my understanding by the Spirit of the Almighty, I discovered that the person whose skeleton was before us was a white Lamanite, a large, thick-set man, and a man of God. His name was Zelph. He was a warrior and chieftain under the great prophet Onandagus, who was known from the Hill Cumorah, or eastern sea to the Rocky mountains. The curse was taken from Zelph, or, at least, in part-one of his thigh bones was broken by a stone flung from a sling, while in battle, years before his death. He was killed in battle by the arrow found among his ribs, during the last great struggle of the Lamanites and Nephites.
More clarity to the story was giving in the footnotes of the publication as follows:
According to Elder Kimball’s journal, the facts concerning the person whose bones had been found in the mound were not revealed to the Prophet Joseph until the camp had departed from the mound. He says:
“While on our way we felt anxious to know who the person was who had been killed by the arrow. It was made known to Joseph that he had been an officer who fell in battle in the last destruction among the Lamanites, and his name was Zelph. This caused us to rejoice much, to think that God was so mindful of us as to show these things to His servant. Brother Joseph had inquired of the Lord, and it was made known in a vision.” (Times and Seasons, vol. vi, p. 788.)
Book of Mormon lands here are specified as being between the Rocky Mountains and extending all the way to the Hill Cumorah or the Eastern Sea. It seems that the specified Eastern Sea is most likely Lake Ontario.