There are gold mines at Castamere. The Reynes were the richest and most powerful house sworn to the Lannisters until their lord, a noted soldier and commander who was called the Red Lion of Castamere, rose in rebellion along with the Tarbecks of Tarbeck Hall. Lord Tytos Lannister was amiable but rather ineffectual, and it seems his young son and heir Tywin was given or took upon himself the task of putting down the trouble. He did so with ruthless effeciency, destroying the house entirely so that its line was ended. There is even a song about their uprising and destruction called, “The Rains of Castamere”. The ruins of their castle stand as mute testimony to Tywin’s justice.
Information about House Reyne that reveals spoilers from the books.