Eric looked out the window early this morning to see an Eastern Fox Squirrel (Sciurus niger) walking along the fence and climbing up a nearby tree.
At first, the orange coloration below made us think about Douglas' Squirrel (Tamiasciurus douglasii), but this squirrel was larger. And later when reviewing the identification, I noticed the orange ears, bushy tail, and lack of black line between the gray on the back and the orange below — characters which led to Eastern Fox Squirrel.
Since I'm relatively new to California, I don't know the entire story of how Eastern Fox Squirrels made it to the West Coast. I hear they were introduced to the Los Angeles area in the early 1900s, and possibly to San Francisco in the late 1800s.
P.S. If you're interested in comparing squirrel species, review the post from 4 December 2012 to see some photos of a Douglas' Squirrel in Sebastopol.