Robert Indiana kept a series of illustrated journals during the late 1950s and 1960s, in which he discusses the development of his work as well as his daily life on Coenties Slip.

His journal page for June 28, 1961, features a sketch of Hardrock, a 24 x 22-inch oil on canvas painting. A note to the left of the painting indicates that the work is in the collection of the artist. Indiana returned to the page almost thirty years later to add the comment "Sold: Simon Salama Caro London 1990."