Weightless in San Luis Potosi Dec 21, 2017 10:15 am by Jeremy TiemannNatural History Survey Share on Facebook Tweet Email Tiemann snorkels in Rio Valles at Mecos Falls. Photo by Tom Miller Images Field biologist Jeremy Tiemann describes a recent trip to the Valles River basin in the Mexican state of San Luis Potosi to collect freshwater mussels. Share on Facebook Tweet Email