Here is an excerpt from John Campbell's Book: 'Mazinaw Experience' available from the CDHS online bookstore http://www.cloynepioneermuseum.ca

'Flora was particularly taken with the democratic ideals of the American poet, Walt Whitman and founded "The Whitman Club" at Bon Echo in his honour. During the years covering WWI, Flora's interest in Whitman's poetry grew until it took on mystical connotations. She saw in this poet a spokesperson for the ideals of freedom, equality and democracy. While the poet had died in 1892 and, thus never visited Bon Echo, Flora corresponded on a regular basis with his official biographer, Horace Traubel of New York. He soon became a frequent visitor.
Trauble would die at Bon Echo two weeks after the dedication of the "Old Walt" inscription in August 1919. It would be the following summer that the actual inscription was cut into the Rock."
Horace Traubel's name is inscribed on "Old Walt" along with Flora MacDonald.
It is unknown what the connection is between Horace Traubel and Colonel Cosgrave and George Morris except all were devotees of Walt Whitman and were likely members of The Whitman Club of Bon Echo and The Whitman Fellowship of Toronto.

Colonel Lawrence Moore Cosgrave DSO & Bar (August 28, 1890 – July 28, 1971) was the Canadian signatory to the Japanese Instrument of Surrender at the end of World War II. In World War I he served as a junior artillery officer in the Canadian Field Artillery in France. Cosgrave was awarded the Distinguished Service Order first in 1916 and again in 1918; later Cosgrave was presented with the French Croix de Guerre. Cosgrave stated that the poem "In Flanders Fields" by fellow Canadian and friend Lieutenant Colonel John McCrae was written upon a scrap of paper upon the back of Colonel Cosgrave during a lull in the bombings on May 3, 1915 after he witnessed the death of his friend, Lieutenant Alexis Helmer, the day before. The poem was first published on December 8 that year in Punch magazine, London. The Colonel John McCrae Memorial, was opened on the 5th. October 1963, by his friend Colonel Lawrence Moore Cosgrave D.S.O.

More information can be found in The Sunset of Bon Echo which can be seen in text form here: