EJ, I believe that was Murdo Mc Kenzie. The town of Murdo was named for him. Part of the country he ran on was north of the town of Murdo. Not too long ago, there still was an old log cabin standing that those old-timers used.
Found a bit about Cap Mossman in the Roundup Years, Old Muddy to the Black Hills book. This was from the Argus Leader and written by Laurel Gray. "The largest cattle ranch in South Dakota was started by a cowboy who once controlled the entire county of Armstrong and had 50,000 head of beef roaming (can't resist pointing out that even back then, ranchers realized their cattle were "beef" on the hoof) roaming about his domain.
The colorful cowpuncher was Capt. Burton C. Mossman and the ranch was big Diamond A, located in Dewey and Armstrong counties. A member of the tough Arizona Rangers, Capt. Mossman was thrust among the reckless, dangerous characters of the west and became the source of many heroic tales of courage. The shipping point, Mossman, was named after the brave cattle owner, although it is no more than a spot on the map today."
I'm not certain "Mossman" is even on current maps. I personally do not know where it was. Will see if I can find out.
Isn't there a barn on the south side of the Cheyenne River bridge on hiway #63 that carries the diamond A brand? Haven't been by there in quite a while.
MRJ