The Collaborative International Dictionary of English v.0.48:

Puerco \Pu*er"co\, n. [Sp.]
   A hog.
   [1913 Webster]

   Puerco beds (Geol.), a name given to certain strata
      belonging to the earliest Eocene. They are developed in
      Northwestern New Mexico, along the Rio Puerco, and are
      characterized by their mammalian remains.
      [1913 Webster]