Early Automobile Map Discovered

 A few years ago I purchased a book at a Garage Sale. Richard Carvel by Winston Churchill. Inside this musty old book I discovered an early road map of  Rensselaer County and Columbia County in upstate New York. It was only a partial part of the total map. I surmise this map is circa 1920's. What I have been wondering about off & on for a couple of years is why certain parts of the map are circled in pencil. All circles are next to a body of water. Along the Hudson River and  three streams are high lited. One spot which is located in the now Schodack State Park has the notation" easy turn off." One spot along the Moorenden Kill stream has the same notation. I think after some research and visiting some of the sights I may have an idea what this map was used for. Obviously, for navigation , route 9J was once a major road to NYC area. I believe the notations show places where one could pull off into the water and cool off ones tires. You see back in those days tires were rubber based , it would be several years before they would not be made of pure rubber. Ford Motor Company  had their own rubber plantation in South America. Rubber was an important product in those days. The biggest problem with pure rubber tires is they could heat up to be as hot as the roadway and in some cases burst. From late spring to early fall . this was a problem. By driving your car into a stream or river could cool your tires off and give you prolonged tire life. This map , probably used as a book mark is rapidly deteriorating. Once exposed to air it has greatly faded. Time for it to fade into history.