Book 3

Cliff-Hanger

by Gloria Ferguson Skurzynski

Published 1 October 1998
Twelve-year-old Jack and his younger sister visit Mesa Verde National Park, where they delve into the park's history while gradually uncovering the mysterious past of their family's teenage foster child Lucky.

Book 6

Ghost Horses

by Gloria Ferguson Skurzynski

Published 1 October 2000
Award-winning mother-daughter writing team weaves science and mystery into thrilling tales set in various national parks
-- Books feature clever young sleuths and fast-paced plots that keep kids turning pages
-- Each mystery involves the featured park's wildlife
-- Park map helps readers follow the action
-- Presents teens in a positive light and promotes good family values
-- A popular series represented on several state reading lists