Why are places like California, Arizona and Nevada less diverse than some midwestern states?

I have gone to San Diego, California, Reno Nevada, and Arizona while visting my mother's family. I always see some Hispanics Indians more asian and people who I don't recognize their race, but I don't see too many black people. Why aren't there many black people there? I have gone to Chicago. I live in Grand Rapids. I visited my dad's family in Evansville Indiana. There was always a good sizeable amount of black people in these places. Can anyone tell me why this is?