While I was in the archives in Bergen County's archives room in One Bergen County Plaza in Hackensack this week, I went through an 1876 Bergen County atlas and found a map that includes what is now the State Line Lookout.
As you may know, the Tappan Zee or ("Tappan Sea") was likely named for the Tappan Native Americans who were Lenapes, the Dutch word for "Sea."
Hard to tell from the map, which includes a line denoting the nearby New York and New Jersey border, but the stretch of the Hudson River near the hawk watch may have been part of what was once called the Tappan Sea. The Hudson itself was also called the North River (as opposed to the East River)
(A thank you to County Archivist Elizabeth Shepard for her help.)
To read more about the old Tappan Zee, and why it was built on a muddy river bottom at one of the widest points in the river -- defying all logic -- read this article:
To look at a great online copy of the map, Eric Nelsen, the historical Interpreter for the Palisades Interstate Park in New Jersey, suggests this link to the original map: