The Mission San Gabriel Arcángel was founded by the Franciscans in 1771, although the current building was built in 1776 after the original was destroyed by a flood. It was a church until 1834, when it fell into disuse, and was then restored by the Claretians beginning in 1862. It is one of the most important historic church buildings in California. Early Saturday morning, around 4 am, it was in flames; the roof has been destroyed and much of the church interior by the fire. Contrary to the somewhat misleading AP report, the mission was not itself founded by St. Junipero Serra, although he was president of missions and thus supervisor for those who did found it; but the mission has had repeated problems the past few years with their statue of St. Junipero being vandalized, and given the recent spate of vandalism against memorials (including several statues of St. Junipero elsewhere), they recently moved the statue to protect it.
It is at present unclear whether the fire was accidental or arson. Either way, it is a great misfortune.
Perhaps I should take some time to listen again to the "Christmas at Mission San Gabriel" episode of The Romance of the Ranchos (found here at #16).
ADDED LATER: The parish is collecting donations for its Fire Restoration Fund.
ADDED LATER 2: It looks like some good news is that almost all paintings and artifacts had been removed to allow some renovating before the mission's 250th anniversary next year. The investigation has so far indicated that the fire started in the choir loft, but isn't giving more than that yet.