The patron himself has declared it.

For the medalla oro and also for a prize will they fight; and the prize--what think you, Senor ?" Valencia, a-quiver with eagerness, laid a slim hand upon the braided front of Dade's close-fitting buckskin jacket.
"The prize will be Solano! That beautiful caballo--beautiful even as thy Surry--which the patron has not permitted rawhide to touch, except for the branding.

Like the sunshine he is, with his hair of gold; and the tail that waves to his heels is like the ripples on the bay at sunrise.
Who wins the duelo shall have Solano for his own, and shall ride him before all the people; for such is the patron's word.

From his own lips I heard it! Me, I think that will be the greatest sport of all, for he is wild as the deer on the mountain slopes--that yellow caballo, and strong as the bull which the patron will choose to fight the grizzly he will bring from the mountains.
"Listen, Senor! The mother of Solano was a she-devil under the saddle, and killed two men by throwing herself upon them; and the sire was Satanas, of whom stories are told around the camp-fires as far south as San Luis Obispo.
"Ah, he is wise, the patron! 'Then let them also prove their courage in other ways.

Let the victor pray to the saints and ride Solano, who is five years old and has never felt the riata since he left his mother's side--who was a devil.' Me, I heard the soul of the patron speak thus, while the lips of the patron said to me: "'Go back to the rodeo, Valencia, and proclaim to all that I will give the grand fiesta with sports to please all.