There's a similar memorial on the White River in VT at the Tweed River junction pool. I was just thinking about this recently when driving by as 2 years ago Hurricane Irene doubled the width of the river bed and likely washed it all away.
Back in wilder times, I went to Carley Simon and James Taylor's house on the Vineyard.
I knew their "au pair" and she had invited us to a party
Turns out it was wrong day, wrong house, wrong party
Lets just say that it was good thing nobody was home.
We hung out on their beach for a while, then left
On the way out when we dropped the car muffler in the driveway. The caretaker then discovered we were there and escorted us the rest of the way off the property.
As for "You're so Vain", supposedly it could have been anyone of 4 guys.
Mick Jagger, Cat Stevens, Warren Beatty, and Kris Kristofferson as she was involved with each of them at some point.