As I understand it, John Morgan went to Preston, Idaho, to visit his third wife, Mary Morgan, who was in hiding there due to the polygamous persecutions of the time, and to see their three sons, Linton, Harold, and one-month-old Mathias Cowley Morgan. Mary must have been staying with the Cowleys.
While in Preston, Morgan suffered an attack of “Typho-Malarial fever”, probably a relapse of malaria due to infection during his service as a Union soldier in the South or during his time as President of the Southern States Mission. He died at the age of 52, leaving three families, one in Salt Lake City, where he had established his college; one in Manassa, Colorado, where he had settled so many converts from the Southern States Mission; and the family in Preston, who returned at that point to live with Mary’s parents in Nephi, Utah.
Matthias Cowley served as a member of the Quorum of the Twelve from 1896 to 1911. He was removed from the Quorum for opposing the Manifesto (termination of the practice of plural marriage). Almost a decade after John Morgan's death, Cowley reportedly performed the post-Manifesto plural marriage of Morgan's widow Mary Linton Morgan to David King Udall. I have seen the location of this marriage listed as being performed either in Preston, Idaho, or in Mexico.