Rock Creek Trail/Beach Drive in MD

I am mapping out a century for myself. I am planning on getting on the Rock Creek Trail at Cedar Lane about 5 miles north of the DC border

https://www.google.com/maps/place/39°00'43.6"N+77°05'28.3"W/@39.0121061,-77.0922783

I see a "trail" there and many references to the trail but I also read...