User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-6064271-20130608181112/@comment-6064271-20130608235037

Thats what i mean when I said that Percy mentions Zoe from time to time. You are right I also noticed that nobody in Camp Jupiter was at Hoover Dam at the time but remember Annabeth was at Camp Jupiter when he made that inside joke and she was in the 3rd book though she wasnt at Hoover Dam