California Pistachio Varieties
California pistachios originated from Iran but they have evolved to be much different in size, flavor, and texture since being imported here to the US. However, there are only a handful of pistachios varieties in California. They vary ever so slightly on size and harvest yields, but overall, it's difficult to tell one variety from the other based on taste, color, or texture. Taste differences are usually due to agricultural techniques, climate, and soil nutrients. The main varieties are Kerman, Golden Hills, Lost Hills, Randy and Peters. Kerman is the most popular variety with Randy and Peters being popular for pollenating.
Please take a look at the pictures below (first 4 photos are courtesy of UC Davis). If you'd like to learn more about California pistachios, here's a publication by the University of California at Davis: