As of 2006-04-30 , the First navel orange tree:
"Riverside
It's still there, growing at the corner of Magnolia and Arlington avenues in Riverside, the mother of all navel oranges. But forget the miracle of the tree, planted in the 1870s. Think instead about the land rush it started. On postcards and orange crates, its Edenic and well-watered simplicity sold and transformed the Southern California landscape."
But I would add:
"Bidwells Bar is an example of the type of oranges that were most commonly grown in California before the Washington navel orange arrived on the scene. The original Bidwells Bar tree was planted in 1856 in Butte County, California and is often called the Mother Orange Tree. It is still alive and is believed to be the oldest living orange tree in California."
http://www.alumni.ucr.edu/50th/index_citrus.html