Mount Diablo

Mount Diablo is a mountain in San Francisco near The Bay Area. It's where Athena trapped Enceladus in the mountain. In The Lost Hero Gaea freed Enceladus from Mount Diablo, and Enceladus uses the mountain to imprison his enemies like Piper's dad, Tristian McLean. Jason, Leo, Piper, and Coach Hedge, went to Mount Diablo to free Piper's dad. Jason killed Enceladus and re-trap him in the mountain.