Complex sentence: The theater was only found in the early 1970s due to a landslide, this caused a major archeological excavation, including the removal of some 4.5 m of earth covering what was left hidden by the landslide.
Split into simpler sentences: The theater was only found in the early 1970s due to a landslide. This caused a major archeological excavation, including the removal of some 4.5 m of earth covering what was left hidden by the landslide.