Galeamopus was first known from a partial skeleton discovered by fossil hunter William H. Utterback in 1902 near Sheridan, Wyoming, in the Red Fork Powder River Quarry A. In 1906, the skeleton was referred to Diplodocus by William Jacob Holland when he described its braincase.[2] The specimen was classified by Holland as a new species of Diplodocus, Diplodocus hayi, in 1924. The specific name honoured Oliver Perry Hay.[3]