Quest in Yosemite National Park: A Mystery Adventure

The fifth installment in a ten-book series.

Before leaving on a two-month summer vacation, Jake Evans finds a gift from his deceased grandfather that will lead him on a scavenger hunt through ten of America's most rugged, wild, and beautiful national parks.

Secret Codes, Lost Landmarks, Hidden Clues, Real Locations. 

ATOS rating of 4.8, that means the book is perfect for 4th and 5th graders, but might also be a great fit for younger and more advanced readers. It's been used in classrooms from 3rd grade up to 8th, which means it is both accessible and appeals to a wide range of ages.