At the start of the Rival’s turn, flip one of the face-down Rival Rancher Cards. The card lists a Rancher icon with a letter. Place that card above the Action Mat with the matching letter.
When you assign your own Ranchers, you must first check if there are Rival Rancher Cards placed above an Action Mat. For each card above, every action space on that Action Mat is considered to have a single Rival Rancher on it. Just as in a regular game, the Occupied Action Spaces rules apply.