Complex sentence: The committee preserved the Towers independently until 1975 when the site, for the purpose of guardianship, partnered with the City of Los Angeles, which in turn partnered with the State of California in 1978.
Split into simpler sentences: The Committee preserved the Towers independently until 1975 when for the purpose of guardianship, they partnered with the City of Los Angeles,. The City partnered with the State of California in 1978.