Complex sentence: The rock spire of Lizard Head looks like an old eroded volcanic plug but it is actually composed of extrusive volcanic ash flows of Oligocene age resting on older sedimentary rocks of Eocene age.
Split into simpler sentences: The rock spire of Lizard Head looks like an old eroded volcanic plug. However, it is actually composed of extrusive volcanic ash flows of Oligocene age resting on older sedimentary rocks of Eocene age.