I don’t think about California for orange production after years of Florida marketing while I was growing up. According to United States Department of Agriculture Florida produces almost twice as many oranges as California, but California still produces a very large number.

Irrigating an Orange Grove, California
Irrigating an Orange Grove.
Southern California already supplies the American Market with nearly 80 per cent of the entire orange demand and promises within a very few years to not only increase this percentage but to extend its markets throughout the entire civilized world.
A few years ago the surface of this great natural park was a wretched waste of cacti and sage brush, the haunt of the tarantula and rattlesnake. Warmth, equable climate, sunshine, absence of frost and generous soil, this section had naturally, but insufficient water. The average rainfall is slight and is confined to a few days in the winter months. The mountains gather up the rains as they fall and send them downward in rushing torrents to the vast reservoirs which are now constructed to hold the excess water in check. From the reservoirs the water is piped down the valleys to the fruit ranches. At the entrance of every ranch is a meter which measures the quantity used. The payment for rental is placed at a certain rate per inch which means as much water as will run through a hole one inch square in one hour. The pipes are opened several times a year and the water allowed to flow between the rows of fruit trees in little rivulets. Moisture and strength is thus given to the roots making fruit growing possible in a region which would otherwise be a desolate waste.
Even now in southern California are vast areas baking in the sun and barren except for cacti, and water is only needed to make them teem with fruitfulness.