Desert Giant

The Mystery of the Desert Giant or the Hardys in California. 

This is not a bad story either in it's original form or in its UK remake. The boys are tasked with finding a missing industrialists son. One Willard Grafton. He and a friend were last seen in southern California, and their plane found in Blythe out in the desert near the desert giants.  

A trip out to Cali with Chet Morton finds that there is a ring running counterfeit cheques out of Mexico and that somehow Grafton is mixed up in this. Chet's latest hobby, Infra Red Photography, is also part of the story, and yes, he does get to use it out in the desert. With a photo of the crooks and such. 

The most notable thing about this is that most of the geography is actually based on real places. The giants exist and are something of a mystery of ancient American folk art. As well as most of the towns and villages stateside being real places, it includes the places for their brief foray into Chihuahua state when pursuing Grafton into Mexico. 

You can read both versions here and here.