Complex sentence: From 1972 to 2003 the hotel/casino was owned by Elsinore Corporation, a wholly owned subsidiary of the Hyatt Corporation until 1979, when it became an independent company.
Split into simpler sentences: From 1972 to 2003 the hotel/casino was owned by Elsinore Corporation. Elsinore was a wholly owned subsidiary of the Hyatt Corporation from 1972 to 1979, when it then became an independent company.