I recently read a great book on this: The Mezcal Rush by Granville Greene, who toured around Mexico getting to know the people making good Mezcal in tiny villages. It's an amazing story. One producer he visited has their pit and still halfway up a small mountainside, next to a water source they like. They have to carry everything up and down the mountain on dirt paths.

All mezcal is made by burying the agave in a firepit; a few still crush the agave with wooden clubs, ferment it in a cowhide hung between trees, and distill it in a clay pot. There's archeological evidence that people there were doing the same thing at least 500 years ago.

I picked up a bottle from Del Maguey, the first company to import "single village" mezcal to the U.S. (prior to that mezcal sold outside the producers' villages was mostly mixed into low-quality blends). It was from that mountainside producer. I wasn't a huge fan at first but it grew on me. There's a lot of taste variation between different mezcals, partly since they don't all use the same species of agave.