We retrieve oranges and grapefruit from trees just dropping them on the ground here in Phoenix. Unfortunately, some of the orange trees have nasty tasting fruit.
Don't forget limes and lemons.
As long as the fruit is on the street and not damaged, it's ready to eat.
Most of the oranges along the streets, at least in Tucson, are sour oranges. They’re good for marmalade, but that’s about it.