Complex sentence: Ross-Loos was so successful that the first small medical office on Grand Avenue in (Los Angeles) expanded into an enormous organization with nineteen medical offices and a large multi-specialty hospital on Temple Street in Los Angeles by 1979.
Split into simpler sentences: Ross-Loos was so successful that the first small clinic expanded into an enormous organization. Besides clinics, the plan had nineteen medical offices and a large hospital on Temple Street in Los Angeles by 1979.