T.O.M. - Top of the Mountain. WW&F #9 runs around her freight on the newly constructed siding at Top of the Mountain. This location is summit of a 3% grade that was the steepest on the original railway. Southbound trains would often have to stop at the bottom of the hill and bring their consist to the top in sections, because the line typically didn't have helpers available. The practice was called "doubling the hill" and was probably quite time-consuming. A siding was provided at the TOM location, where the train could be re-assembled when the process was complete. Today, TOM is the northern terminus of the museum's trackage, although there are plans to continue building to the north.
By the way, if the pine trees in the background look like they are sagging just a bit, it may be from the weight of the ice that had accumulated as the result of freezing rain earlier in the day.