In the book Printmaking in New Mexico author Clinton Adams notes: "Many of Cassidy's early lithographs were printed by the Latham Litho & Printing Co. of Long Island, NY. By 1918 or 1919, however, he had his own lithography press and stones in Santa Fe and did much of his own printing." (P. 143.)
Judging by the clothing and hairstyle, this appears to be a person of Southwest American Indian descent, perhaps Tiwa (Pueblo) or Apache. At the time of this lithograph's creation, Cassidy had been living and working in Santa Fe since 1912, but had already spent several years in an Albuquerque sanitarium after contracting pneumonia in 1890, needing the drier climate to recuperate. He developed a love of the Southwest and returned once he had reestablished himself as a professional artist.