The wine industry in Sonoma County and the Napa Valley is especially well known. This year (2017) the fires ravaging through Northern California did a significant damage to the wine industry there, so the price of California wine may be higher in years to come.
The farming industry is so important that there are all sorts of rules and regulations about bringing food into California from other countries and even other US states.
Rules are actually enforced. Even in the Nevada-California border there is some “strawberry police”, and you can pay hefty fines, or even be thrown in jail for trying to smuggle strawberries into California. This is to prevent importing diseases and pests that could decimate local crops.
It is a big state with a large population. Just to give some idea, more people live in the State of California than in the entire country of Canada. Which is does not help traffic congestion a bit in densely populated areas.