Planted 1830. The building around it fell down and was put back. All records sourced and cited.

In 1830 a sailor up from Peru handed over some seeds at Mission San Luis Rey, and Father Antonio Peyri planted them.
The mission's own account of it is plain. "The first pepper trees in Alta California were planted by Fr. Antonio Peyri using seeds brought to San Luis Rey in 1830 by a sailor from Peru." The mission says the tree standing in its quadrangle today is the oldest living pepper tree in California.
Here is the part worth sitting with. The building that tree was planted beside fell down around it. By 1887 the mission was a ruin, roofless in places, its adobe washing away. The tree was still there.
Three things before the story runs. In 1825 two thousand eight hundred and sixty nine people lived at this mission, which is more than three times the California average. By 1830 it was the largest building in California. And in that same year Peyri put up a memorial to the Luiseño who built it.
Father Lasuén founded San Luis Rey de Francia on June 13, 1798. It was the eighteenth of the twenty one California missions and it was built on a scale none of the others matched.
The plan was the usual one, a church with the padres' quarters, shops, storehouses and granary arranged around a large open court. The federal survey of the place puts the difference bluntly: it was built "upon a larger scale and more pretentious than any of the others except possibly that at Capistrano."
The quadrangle runs about five hundred feet on a side. The whole complex covered six acres.
The foundation of the church that stands now was laid in 1811 and the building was finished in 1815. By 1829 a dome had gone up over the crossing and the wall and ceiling decorations were done. More work went onto the sacristy and the church in 1832.
Field stone foundations. Adobe walls, with burned brick for the pilasters, the mouldings, the belfry, the dome over the mortuary chapel, the altars and the arches, all of it plastered over. A wood roof under tile.
The federal survey names who did the work in the language of 1936: "Indians and Mission soldiers under direction of Padre Antonio Peyri."
The mission's own language is more specific. The Indian Memorial that Peyri erected in 1830 honors, in the mission's words, "the many Luiseños who helped build and maintain the Mission, including those who lived in outlying areas such as Pala, the asistencia or sub-station to Mission San Luis Rey."
Two thousand eight hundred and sixty nine people were living at San Luis Rey in 1825.
That is the figure that explains the rest of it. The buildings are that large because the population was that large. More than three times what a California mission typically held, in one place, in the San Luis Rey valley, fourteen years before anybody had drawn a line on a map and called it San Diego County.
By 1830 it was the biggest building in California.
The mission system ended, the population went, and the buildings went with it.
Through the second half of the nineteenth century the padres' quarters and the dormitories fell into ruin. The granary, the shops, the storehouses, most of the quadrangle, gone.
In March 1887 Herve Friend set up a camera in front of what was left for Douglas Gunn's book about the county. The photograph shows the church with its bell tower still standing over walls that are visibly coming apart, roof gone in places, the adobe exposed and eaten back, and the long cloister arcade trailing off to one side.
That is what the place looked like after eighty nine years.

Father O'Keefe began work in 1892 on a church the federal record describes as having been in a much ruined condition. It was rededicated in 1893.
New padre quarters and dormitories went up in 1898 in place of the structures that had collapsed. The dome of the church was rebuilt in 1930 to plans by Lescher and Mahony, architects out of Tucson.
When Henry Withey photographed the mission for the Historic American Buildings Survey in November 1936, what survived of the original complex was the church, a number of the cloister brick arches, and the ruins of a few walls. Everything else in his pictures had been put back.

The church, restored. The arcade. And in the quadrangle, the tree.
The San Luis Rey valley is the reason Oceanside is shaped the way it is. The river runs out of the back country to the ocean, the mission went where the water and the people were, and the road and later the rail line followed the same corridor because it is the flattest way through.
Inland Oceanside is still organized around that valley, with the river and its floodplain running through the middle of it. Floodplain is a permanent feature of a parcel and it is mapped. If you are looking at anything in the valley bottom, that is the first thing to check and it will not change with the market.
Current numbers are in the Oceanside market report, and the wider area is in North County Coastal.
The tree claims belong to the mission. That these were the first pepper trees in Alta California, and that the one in the quadrangle is the oldest living pepper tree in California, are the mission's own statements about its own grounds. This piece quotes them and attributes them. It does not independently establish either.
Whose labor, and on what terms. The federal survey of 1936 says the mission was built by "Indians and Mission soldiers." The mission's own memorial, erected in 1830, names the Luiseño. Both of those are quoted here. Neither source describes the conditions under which that labor was given, and the question of how free it was is a serious one that these two documents do not answer. This piece does not pretend they do.
The largest building claim. "By 1830 the mission was the largest building in California" is the California Missions Foundation's statement. It is a reasonable claim about a six acre complex in a province with few large buildings, and it is reported here as theirs.
What the 1887 photograph is and is not. It is the mission in March 1887, five years before the repairs started. It is not a photograph of the mission in its working years, and nothing in this piece should be read as showing the place as it stood when nearly three thousand people lived there.
More San Diego history: stories from around the county, one place at a time.