Pretty sure this is a garter snake but I don't know the exact species. It was light grey and most of the others I've seen here are darker. Found it in a pile of dried grass shavings.
En boñiga de caballo muy degradada (con paja expuesta) en un sitio muy húmedo (encharcado) a media sombra. // In very degraded horse dung (with exposed straw) in a very humid site (next to a puddle) in partial shade.