"They had been completely around Big Thumb. It was like a giant sundial. They followed the shade"
A modern sundial
GNU Free Documentation LicenseA modern sundial - Credit: SEWilco / Wikimedia Commons

A sundial is a device that tells the time based on the movement of the sun. The flat surface is marked with lines indicating the hours, and a rod or triangular protrusion called a gnomon rises from the centre to create a shadow.