Location: Ventura County, California

Named after a Saint William (there once were many), all of whose deeds are now so dimly remembered that they're no longer venerated. For example, the Catholic Archdiocese of Los Angeles checked and can't find even one in their liturgical calendar. There were however an abundance of Medieval monks, and scholastic theologians of that name: (William) -de la Mar (ca. 13th C), of Auvergne (ca. 1180-1249), of Auxerre (ca. 1150-1231), of Conches (ca. 1100-1154), of Hirsau (ca. 1025-1091), of Moerbeke (ca. 1250-1286), of Saint-Thierry (ca. 1085-1148), and of Tyre (ca. 1130-1185). Whoever it might have been, Jim Blakley notes that there was once a Ventureño (Chumash) Indian summer rancheria named San Guillermo at nearby Pine Spring just to the East of this summit. A friar may have given it this name when he first came upon this village--most likely at about the time of the Saint's feast day. In the days before the natives were forced to live (and die) at the local mission, this was a common way of designating an Indian rancheria and almost any other sort of new place name. This name was some time afterwards extended to the mountain.

Variant names include Ray's Peak, given for unknown reasons on Wheeler Survey Atlas Sheet 73 (1871) and on the California State Mining Bureau Preliminary Map of California (1891), also called "Mount San Guillermo" on original HPS List.

Name first appears on GLO Santa Barbara National Forest (east half) map (1918).

Peak was on the original 1946 HPS Peak List.