The Piedra river canyon in the vicinity of the Monasterio de Piedra is a place of extreme natural beauty, a lush, garden-like environment of waterfalls, mosses and rivulets in the midst of an arid wilderness. A marked and fenced path winds its way through the course of the canyon, with overlooks of several waterfalls; the longest and most notable of these is the "Horsetail" (Cola del Caballo), at more than fifty meters high. These waterfalls are formed by the precipitation of dissolved limestone that occurs when the decreasing river level exposes rocks to sunshine; this results in water evaporation and deposits the limestone in successive layers through which the water runs, forming countless rivulets