This species is highly variable (more than 90 infraspecific taxa have been described), not only among different plants and locations but also within individual plants over the course of the growing season, especially in petal size and color (see W. L. Jepson 1909-1943, vol. 1, part 7, pp. 564-569).
Native Americans used Eschscholzia californica (no varieties specified) to treat lice, to induce sleep in children, as a poison, for consumption, for toothaches, and as an emetic (D. E. Moerman 1986).