Bret, somewhere in the information you gave me, there is a piece of Oregon Lumber Company propaganda that does show a wye track surrounding the mill site at Bates. The west leg went between the mill building and the lumber sorting building (I am guessing what the big building just west of the mill was for), the east leg was north of the lower pond and the main SVRy line was south of the lower pond. The engine repair shed you mentioned would have been near the northern junction inside the wye.
Brian