I've seen quite few references to journals of Brigham Young. That made me wonder if he did keep any journals at all. I found an article by Dean C. Jessee:
The Writings of Brigham Young (Western Historical Quarterly, Vol. 4, No. 3 1973, pp. 273-294).
Dean Jessee writes:
The most significant source of information on the life of Brigham Young is the collection of his papers filed in the archives of the Church of Jesus Christ of Latter-day Saints in Salt Lake City, Utah. This collection, comprising more than a hundred boxes of records, contains the 47,735-page manuscript history of Brigham Young, twenty-one volumes of letter books totaling 15,000 pages, four personal diaries, nine office journals, seventeen boxes of loose papers (rough-draft letters, addresses, certificates, and other documents), several thousand items of incoming correspondence, four volumes of telegram books, and numerous records pertaining to Brigham Young's business holdings - not to mention the voluminous printed works and manuscript collections related to him.
A hundred boxes of records sounds a lot. However, that includes only four personal diaries. The article continues:
Of an estimated 70,000 pages authored by Brigham Young in the church archives, fewer than 425 were written in his own hand.
Well, that doesn't sound a lot.
Later in the article we read:
British Mission Writings. Two of Young's diaries and fifteen letters, containing more than half of his personal writings, record his British mission experiences of 1839 to 1841.
So, there is a chance that Brigham might have written something about "Prophets Barn". I assume those diaries are in the Church Archives.
I assume this would be the relevant diary:
https://dcms.lds.org/delivery/DeliveryM ... =IE4093039