Thanks to Brent Murray for posting this on the Facebook Page:
Here’s a map of Washington Heights from 1874, which was about 15 years before it was annexed into the city. It looks as though the land owner’s names were part of the map. Its shows the Rock Island’s Dummy Line (that is what it was called) running down 99th. It wasn’t until years later that it became the suburban line and went to 89th and reconnected with the Main Line at Gresham Crossing. Do any of these names ring a bell?