Triple Pennsy Diesels at the Horseshoe Curve

Here's a shot of three Pennsylvania RR diesels pulling a line of freight up to the Curve on track 4. At the forefront of the three is U25B #2525, second is GP7 #8501, and thirdly is RSD15 #8615. This photo is designated prototypically during the late 1960's - prior to the Penn Central transition.