Final answer:
Venters seeks revenge on Oldring due to personal grievances after an altercation with rustlers, the theft, and recovery of valuable horses, culminating in a deep-seated desire for justice and resolution.
Step-by-step explanation:
In the passage provided, the character wishes for revenge on Oldring because of a complex array of emotions and events. This character, Venters, has been through a significant ordeal involving an attack by rustlers, the theft and subsequent recovery of valuable horses, and a race. He also has a personal vendetta against Oldring, evidenced by the line, "What had happened? He had left the valley to go to Cottonwoods. Why? It seemed that he had gone to kill a man-Oldring!" This passage shows a psychological and emotional response to these events, illustrating Venters's desire for confrontation and resolution against those who have wronged him. The need for vengeance appears to be a result of a build-up of personal offenses and the need to assert justice for transgressions against himself and those he is associated with.