Father Fernando Martin celebrated the first mass on September 20, 1818 at a nearby site, an outpost of Mission San Diego. By 1822 Santa Ysabel had a chapel, cemetery, granary, many houses, and 450 neophytes. After secularization in the 1830s, priestly visits were rare. Tradition asserts that services have been held here since 1818, under ramadas erected against one wall after the roof caved in. The present chapel was built in 1924.