The pistachio is native to Turkey and Iran, and those two countries have always provided most of the world's supply. California has the right climate for pistachios, though, and it has become a major pistachio player. Last year, it actually outproduced both Iran and Turkey.
Still, few Californians have ever seen a fresh pistachio straight from the tree. It doesn't look the way you'd expect, because there's a little bit of flesh, about an eighth of an inch thick, surrounding the nut. This bit of fruit has a lurid reddish purple color, and sometimes it stains the pistachio shell a little, which is why it used to be traditional to dye pistachios red.
A fresh pistachio has a slightly crooked oval shape, like a miniature mango (mangoes often get a blush of that reddish purple color too). It turns out the pistachio is actually related to the mango. And though pistachio flesh isn't sweet, it does have a surprisingly mango-like aroma. In Turkey, some people make a sort of jam out of it.
Looking a little further afield, pistachios are also related to poison oak and poison ivy. Mangoes and cashews are closer to the poisonous cousins, so close that they (unlike pistachios) can cause exactly the same kind of rash. Cashew nuts are poisonous until they're toasted, and every part of the mango except the fruit is capable of raising a rash. Some people are so mango-sensitive that they get a reaction from very scent of a mango blossom.