Name That Tuber

At first I thought these were exceptionally uniform rocks so I picked up a rock from the trail and threw it at the pile to see what lind of noise it would make. Theyre not rocks, but some sort of root vegetable. Some of them are as big as bowling balls. 

A km or so after this wall of yams I got to see them being harvested. 

This machine scoops them out if the ground, cuts off the leaves and stashes them in a humongous bin on the machine.  When its full, the driver dumps the bin onto the pile. 

I'm pretty sure potato farming technology has advanced since the days of ancient pilgrims.