Fort Tuthill is just south of Flagstaff off I-17. Click on the map below for a larger version. Go west at turnoff labeled "Pullium Airport and Fair Grounds." (Airport is to the East).
Depending on the event, signs will be often be posted. Weight Pull practice is usually behind (north) of the Race Track and Rodeo Arena. These can be located on the map below (click on it to enlarge): More information about Fort Tuthill Recreation Area is available here: