It is a white over light blue ascending diagonal 2:3 flag with quasi-heraldic emblem over all, showing inside a Chilean-style shield divided per pall reversed a tree (dexter), a cow head (sinister) and some sort of fruit (base). António Martins, 24 August 2024
However, in the Wikimedia Commons the very same Sergio Arenas / Xaruco Ponce uploaded in 2009 (two years after this report), a version of this that is slightly different: 3:4 descending diagona with much smaller emblem, sourced to other examples of local useage: One to a meanwhile vanished website http://www.goredelosrios.cl/fotografias.htm, and the other to http://www.munipaillaco.cl/, the official communal website, which, as mentioned, was meanwhile modified. The emblem is depicted in this 2009 version of the flag in yet another rendition. António Martins, 24 August 2024