First, the UP 18 and 26 are the two surviving turbines. They haven't been moved from their museums in many years and have no prime movers anyway. They look nothing like a U50 either.
There no eight trucked U50's left. They were all traded in to GE in 1974 with the exception of three that ran unti 1977. They were all scrapped and none were donated for display. There is now way an eight trucked U50 could be seen anywhere today.
This only leaves the U50C, with the same general carbody but the D-D trucks. This is what happened to them:
UP 5000 Nov 1969 37139 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in August 1977.
UP 5001 Oct 1969 37140 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in August 1977.
UP 5002 Mar 1970 37141 8 Mar 1977 Wrecked; sold for scrap to Erman Corp., Turner, Kans., in May 1977.
UP 5003 Mar 1970 37142 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in August 1977.
UP 5004 Mar 1970 37143 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in August 1977.
UP 5005 Apr 1970 37144 8 Mar 1977 Wrecked; scrapped by UP at Omaha in August 1977.
UP 5006 Apr 1970 37145 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in May 1977.
UP 5007 May 1970 37146 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in August 1977.
UP 5008 May 1970 37147 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in August 1977.
UP 5009 May 1970 37148 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in May 1977.
UP 5010 May 1970 37149 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in May 1977.
UP 5011 May 1970 37150 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in May 1977.
UP 5012 Nov 1970 37151 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in May 1977.
UP 5013 Dec 1970 37152 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in May 1977.
UP 5014 Dec 1970 37153 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in August 1977.
UP 5015 Dec 1970 37154 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in August 1977.
UP 5016 Dec 1970 37155 8 Mar 1977 Sold for scrap to Erman Corp., Turner, Kans., in May 1977.
UP 5017 Jan 1971 37156 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5018 Jan 1971 37157 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5019 Feb 1971 37158 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5020 May 1971 37273 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5021 May 1971 37274 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5022 May 1971 37275 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5023 Jun 1971 37276 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5024 Jun 1971 37277 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5025 Jun 1971 37278 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5026 Jun 1971 37279 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5027 Jul 1971 37280 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5028 Jul 1971 37281 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5029 Jul 1971 37282 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5030 Aug 1971 37283 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5031 Aug 1971 37284 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5032 Aug 1971 37285 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5033 Sep 1971 37286 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5034 Sep 1971 37287 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5035 Sep 1971 37288 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5036 Oct 1971 37289 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5037 Oct 1971 37290 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5038 Nov 1971 37291 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
UP 5039 Nov 1971 37292 23 Feb 1978 Sold for scrap to Erman Corp., Turner, Kans., in June 1978.
They were all either scrapped or wrecked and none were preserved. None have started wandering the rails again after being cut up in pieces in 1978.
Dallas, I gave no idea what you saw, but it wasn't a U50. The Centennial is the only large engine that was preserved with the prime mover intact and still runs. If it wasn't a Centennial, it's a UP engine I've never seen or heard of, and I've been watching UP trains saince 1965.