The Mystery of Rainbow Gulch (Ted Wilford #12), by Norvin Pallas (epub/Kindle/pdf)
The 12th volume in the Ted Wilford series!
Ted and Nelson stay at Bob Fontaine's ranch. As the boys arrive, a plane crashes, and one occupant vanishes. Meanwhile, a mystery surrounds an old hermit, and footprints indicate that someone has been watching the ranch... An excellent entry in the series!