With a little more sleuthing, this is what I discovered...
Looking east toward the creek and Ames, IA. Back of foto reads, "campus view remedied by plantings ordered by Landscape Architecture, dated March 30, 1917. These are the Sycamores! (fotos courtesy of Parks Library, Special Collections ISU, Ames, IA)
Sycamore Row along the cinder path,1974. This is the same stretch as that shown in 1917 foto above. (fotos courtesy of Park Library, Special Collections, ISU, Ames, IA)
(foto courtesy of dlcooper, 2010) A winter walk along Sycamore Row, 2010, close to the same spot as the above two fotos.
You might wonder, as did I, why Professor Erwin planted Sycamore trees to line this walkway from campus to creek?
I found in his personal papers that he was born and raised in Fulton, Missouri. When I google-mapped Fulton, the first street that popped up was Sycamore Street. A perfect species choice for this stretch of floodplain.