The Santa Ysabel Asistencia was founded on September 20, 1818 at Cañada de Santa Ysabel in the mountains east of San Diego (near the village of Elcuanan), as a "sub-mission" to Mission San Diego de Alcalá, and to serve as a rest stop for those travelling between San Diego and Sonora. The native population of approximately 450 neophytes consisted of both Luiseño and Diegueño peoples. Based on historical records, Santa Ysabel enjoyed a higher-than-average conversion rate when compared to the other California missions.