There is no question of the wye at MP 299.2, 2 miles below Volcano, on the east side of the Chili line as it is also in the valuation maps. Now the question is when it was active in service. It is not shown in the 1888 line sketch of the sidings of the line. Now the question is to find out why it is not shown in the timetable. That may be because it might only been for m/w equipment and not for train crews to use as too sharp and too light rail construction. See at Terraserver.com and work down the line from Antonito.
There are some published books which may show the track inventory status. PRR