Complex sentence: Groundskeepers fed the cats at various locations on the grounds until 1970, when Irène Desormeaux began feeding the cats at the location where the colony became established.
Split into simpler sentences: Groundskeepers fed the cats at various locations on the grounds until the 1970s. In the late 1970s, Irène Desormeaux began feeding the cats at one location, where a colony became established.