Papilio indra pergamus
Edwards's Indra Swallowtail
The subspecies of the rarely-encountered Indra swallowtail from the San Gabriel Mountains down to the mountains of Riverside and San Diego Counties is pergamus. As of 2021, I've seen it a few times in the San Gabriels hilltopping on Sunset Peak; in the San Jacintos near Idyllwild patrolling a high ridge; and at Kwaaymii Point in Anza-Borrego. The type locality was established by Scott Miller in the 1980s as "Devil Canyon, about 11 km NNW of San Bernardino, San Bernardino Mountains, San Bernardino County, California, a well known locality for the subspecies (Emmel, pers. comm.)." I've reproduced his article below as well as Edwards' description of pergamus.
This butterfly is a hilltopper, but it is best to look just below the actual hilltops and along ridges to find indra. The southwestern side of the hill is usually the best place to look. They fly in the spring, and the larvae feed on aromatic Apiaceae family plants, especially Tauschia arguta, T. parishii, and Lomatium lucidum.