That's the old R.O.W. of the former Chicago & Evanston line of the Milwaukee Road not the North Shore Line. The North Shore Line ran on the north side main of the L to access the Loop and is completely unrelated. The last train on the C&E in front of Wrigley actually was much more recent than one would think, 1973, and one could see rails on Waveland as recently as a few years ago.
Here is a good thread of info on the R.O.W.
Here are a couple shots, all of which I believe were taken when Wrigley was known as Weeghman Park:
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Another
here.
Even more information on the C&E
here and
here.