I have to say that this phenomenon seems much more visible and extreme in denser urban areas. I'm an American who has lived in Europe for almost 20 years, and me and my family just completed a 2 week camping trip in rural Colorado and New Mexico and we had a fantastic time. People out in the country and in smaller towns seem to be a lot more friendly and open to getting to know you.
I'm not defending the US as I'm often the first to shit on it culturally, but I would definitely suggest getting out if California tbh.