[1][2][3] Costo had many careers and avocations throughout his life, including farmer, cattle rancher, surveyor, and mineralogist.
[2] He attended Riverside City College in the 1920s along with classmate John Gabbert, who ultimately became a Superior Court Judge.
[4] As part of the same efforts, he and his wife, Jeannette Costo, founded the scholarly journal The Indian Historian as well as the popular press periodical Wassaja.
[3] Costo and his wife Jeannette opposed the efforts within the Catholic Church to name Father Junipero Serra a saint based on the claim that he treated Native Americans in an inhumane fashion.
[2] The Costo Chair in American Indian History at the University of California, Riverside, was named in his honor.