In that busy summer of 1797 for Father Lasuen he found his fourth new mission in a large valley discovered on an earlier expedition. Although this new mission was to close the gap between San Buenaventura and San Gabriel, due to the attractiveness of the valley the mission was actually much closer to San Gabriel. Today its close proximity to Hollywood has allowed it to be used for many movie location shootings.

In a short time the mission had outgrown its first small church and soon had completed the quadrangle with a large church. Barracks, houses for the nearly 1,000 neophytes (Christianized Native Americans), workshops and storerooms surrounded the quadrangle. All buildings were sturdily build and had riled roofs. A large convento (missionary quarters) dominated all these structures. Usually connected to the church, at Mission San Fernando it was added later and stands separate from the quadrangle. It was two stories high, 243 feet long, 50 feet wide, and fronted by a colonnade with 20 arches. This building is the largest adobe structure in California.

In spite of all the precautions taken in constructing the large church, it could not withstand the violent shaking of the 1812 earthquakes. The repairs made to the church afterward were so substantial that it probably would have then stood for a very long tie had it not been to damage done by vandals. After secularization the roof tiles were removed for use in other buildings, leaving the adobe walls unprotected. After the discovery of gold, vandals dug up the church floor looking for buried gold.

Mission San Fernando had over 30,000 grapevines and a wine factory. In addition to the wine they had a large trade in hides and tallow. At its peak there were more than 21,000 head of livestock. The natives were well skilled in leatherworks. They made shoes, clothes and saddles for their own use and for trading. They also made large quantities of rawhide strips that were used in building. Since spikes and nails were rare, pieces of rawhide were used to tie structures together.

Shortly after the mission was secularized one of the earliest gold finds took place on a neighboring rancho. One of the ranchers found shiny yellow particles clinging to the roots of an onion from his garden. Word of this discovery soon spread and the area became overrun with gold prospectors. It was false rumors that the missionaries had been prospecting gold for years that caused gold-seekers to dig up the church floor in search of buried treasure.

With the roof tiles removed from all buildings except the convento, they soon began to crumble back to the earth. The convento was eventually used as a hog farm in 1896. Fortunately the Landmarks Club soon turned their attention to Mission San Fernando. In order to restore the roof to the church before it completely collapsed, they sold candles for a dollar apiece and raised $6,000 to begin the restoration.