Ranging throughout the western third of Oregon, California Ground Squirrels (Spermophilus beecheyi) are much larger and bushier-tailed than other ground squirrels. They are found in open grasslands (including large lawns) and on rocky outcrops. Unlike other ground squirrels, they will also climb trees to obtain food. A colloquial name for this species is Gray Digger.
This individual was on Barview Jetty on the north shore of Tillamook Bay (Birding Oregon p.125). Rocky coastlines are an unusual habitat for ground squirrels. Note the white dapples on the back.
This individual also shows the white speckles on the back. Note the bushy tail edged in white, similar to that of a Eastern Gray Squirrel.
This female with her two young had a burrow at the base of a large tree at the Portland Rose Garden. Notice that when the fur is ruffed up, as on this individual, the white spots are much harder to see, making it harder to differentiate this species from one of the tree squirrels. California Grounds Squirrels can be solitary or live in loose colonies. When living in a colony, each individual has their own private burrow entrance.
Here is the same female eating a leaf. California Ground Squirrels eat a wide variety of plant matter to build fat reserves for their winter hibernation.
Ethical Birder 
I have a spotted ground squirrel eating with my silver grays, but he has a difference. He has a black V-W/white on the outer edges from the neck to back of shoulders. The digger grays in this area, Douglas Co, Or, normally do not even have spots but the V stripe is a new one to me. Any ideas?
According to Mammals of Washington and Oregonby Tamara Eder, “A good diagnostic feature is the V-shaped pattern of light fur that begins at the napeof the neck and runs over each shoulder to the sides. This light-colored ‘v’ encloses an area of much darker brown fur.” That sounds like your critter.
we are over here in Eastern Oregon and have come up on what seems to be a California a ground squirrel. However the one that we have here has a black stripe down its back with white and your pictures of the one on your website don’t have that so we are wondering if its a different kind of squirrel or a hybrid or if it fell into
some black paint? Would love to hear your thoughts on this. I just read the posts below and it sounds like I am asking the same question that they are,so maybe you have already answered our question.
thanks so much
Emile
Emile, Check the response to the previous comment and see if that description matches your critter.