How to avoid extinction

Leo's grandfather died a year ago, and ever since Leo has been tasked with tracking his grandmother down whenever she wanders away from their home in Allentown, Pennsylvania--but when she abruptly decides to take the trip to Utah that her husband was planning, Leo finds himself on the way to visit dinosaurs, in an old Buick with his grandmother, his seventeen-year-old cousin Abby, and Abby's old, smelly Golden retriever, Kermit, without telling his mother.