douglasii vs. beecheyi
The Douglas ground squirrel (O. douglasii) is now being recognized as it's own species separate from California ground squirrel (O. beecheyi).
PDF explainer, https://drive.google.com/file/d/1zaKja9z-rN6tgsJ8dkYy-DQm8YMkcyyo/view?usp=drive_link
The biogeographic split is essentially the San Francisco Bay/Delta, the Sacramento River north to Butte Creek, and generally the area of Butte Creek up toward Lake Almanor. Apparently both species may occur at the north end of Lake Alamanor.
So, north of the San Francisco Bay, west of the Sacramento River, and west of Butte Creek (inclusive of Chico) up through northern California, Oregon, and part of Washington is O. douglasii.
Douglas ground squirrel typically (but not always) have a very dark, triangular patch in the middle of the back:
https://www.inaturalist.org/observations/33233311
https://www.inaturalist.org/observations/192025357
https://www.inaturalist.org/observations/191798961
https://www.inaturalist.org/observations/193557796
https://www.inaturalist.org/observations/185386149
https://www.inaturalist.org/observations/185386151
https://www.inaturalist.org/observations/85297891
