Full disclosure: I read this with a third-grade girl I tutor (she brought it from home), and the "mystery/adventure" plot was less than ideal to read once a week. It was difficult to remember the clues, etc.
Separate from that, the story is just not well executed. I found both the plot and dialogue to be clunky. My student and I found many places to edit punctuation and discuss word choice.
It was certainly a struggle for me to get through it. It might work better as a short story. So much of it feels convoluted, bizarre, and far-fetched that a lot could be cut. I can see how it would be a fun read if you are going to the Grand Canyon yourself because the characters are getting their Junior Ranger badges and visit various real locations, but it's not up to par in an education setting.