Publisher:Parnassus Press
According to a 2011 blog by Peter D. Sieruta, "involved with children's books most of my life, from my earliest days working in the grade school library to my current job cataloging children's books for a university" ("Smud-ged in Earthsea"):
Parnassus Press of Berkeley, California, was established in 1957 by Herman Schein. His wife Ruth Robbins (ISFDB) was one of its writers and illustrators. It may be known best for children's picture books.
Schein solicited A Wizard of Earthsea (1968, ISFDB), which Robbins illustrated, from Ursula K. Le Guin in 1967. It would be a work "for older readers" from the Parnassus perspective, although decidedly a work for younger readers for Le Guin. Parnassus had previously published with illustrations by Robbins a book by Le Guin's mother, the anthropologist Theodora Kroeber (ISFDB): a fictionalized biography, Ishi, Last of His Tribe (1964, Wikipedia).