Smithson created Forking Island in 1971 using paint and marker on mirror to illustrate a formation for an earthwork he planned to create off the Florida coast. In May 1971 Robert Smithson traveled to the southern coast of Florida for three weeks with the intention to make a forking island and an island maze off one of the Florida Keys. While these earthworks remained unrealized, Smithson captured his ideas for the hypothetical islands through drawings and paintings. Forking Island is stylistically similar in mark making to Smithson's drawings for other proposed earthworks at the time, but it is unique in Smithson's oeuvre in its use of mirror as the substrate for a two-dimensional work. Mirrors played an important conceptual and material role in Smithson's work; he often used mirrors in sculptural works, exploring the reflection of the viewer in earlier works like Four-Sided Vortex and in contemporaneous works such as Rocks and Mirror Square II.