I think there's 3 distinct anglo/caucasian populations in Petaluma/Sonoma County.
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People who used to live in The City (aka SF) or East Bay when It Was Cool and have since moved up here.
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People whose families have been here forEVER. Ranchers, farmers, city streets with the family name, etc.
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People who moved here from somewhere else entirely, like me.
No judgment call on any of these.
(*I know nothing about the Hispanic population so I won't speak to that, and Petaluma, at least, seems to have very small african american, asian, south asian, etc population.)