Geography plays a major part. This country has more tornadoes than anywhere else on earth. Location, location, location! We have the perfect battlefield - massive flat plains. Cold air dropping down from Canada on one side and warm moist air moving up from the Gulf of Mexico on the other. All it takes is a "kicker" (a cold front or trough) to get the battle going.
Not all thunderstorms create tornadoes. The must be cross winds at just the right altitude to generate rotation. Hilly or mountainous terrain can disrupt rotation. Even so, tornadoes can happen anywhere on earth. The Central Valley usually sees 2 or 3 tornadoes each year. Most are short lived and do minor to no damage (F0). Thunderstorms in California are usually created by sunshine warming the ground. That’s why they dissipate so quickly once the sun sets. This combined with the steep sides to the Valley limit rotation. Funnel clouds (a tornado that doesn't reach the ground) are a bit more common.
Yes, there’s been a tornado here. Back in the 90s a very strong thunderstorm cell developed down in the Valley in the late afternoon, producing heavy hail and a tornado. Usually thunderstorm cells dissipate as they move up the hill, but this one held together… and brought its (F0) tornado with it. Due to the hilly terrain, the tornado bounced from hilltop to hilltop before dissipating well east of here. I tried to see it, but didn’t. (Yes, I was out running around in a strong t-storm… not the first time.) Numerous funnel clouds have been reported in this area over the years, but again, I never saw any of them (yes, I go out look for them). There are just too many trees! The best view is at the crest of the highway. That place grants a stunning view of the Central Valley all the way to the coastal ranges… with the Sutter Buttes right in the center. However, it’s not a very safe place to stop and tornado watch as its a 3-lane highway at that point and traffic does around 70 mph – rain or shine(65 mph if a highway patrol is present). Other “prime” viewing locations are on private property.