FOUND Surreal children's book

[flowersforgraves]

I am trying to recall a very surreal portal fantasy book I read about 10-15 years ago. I believe it was a children's or young adult book. I don't recall much about it other than the state of Delaware was a fabrication by a sinister power, and possibly also that dinosaurs lived there. The cover of the book was green and yellow, and had a pulpy feel to the aesthetic. I know it's a long shot based on what I recall, but if anyone can help me, that would be great! Thanks.

edit: I'm pretty sure the protagonists were two boys and a girl, if that helps at all.