Complex sentence: After the World's Fair, summer productions languished (usually blamed on Seattle's unpredictable weather) until the Aqua Theater was mostly abandoned--a 1969 concert by the Grateful Dead revealed that the grandstand was crumbling and dangerous.
Split into simpler sentences: After the World's Fair, summer productions languished, which is usually blamed on Seattle's unpredictable weather, until the Aqua Theater was mostly abandoned. A 1969 concert by the Grateful Dead revealed that the grandstand was crumbling and dangerous.