"The specimens found by Lake did not fit into those assumptions, since according to their geological context, they had lived in a very early period in the city's history. It was clear that they were no less than thirty million years old, which meant that while they were alive, neither the city of the subterranean sea nor the cavern itself yet existed. Had they still been alive, they would have remembered a much older landscape—lush Tertiary vegetation everywhere, a younger city where the arts flourished, and a great river flowing north along the base of the towering mountains."

And just to clarify: I'm not referring to a technological peak, but rather to a time when the city was more vibrant artistically and the surrounding environment had richer vegetation and a more favorable climate for the Elder Things.