Martha's Old Mexico Restaurant is a gem of a restaurant in Sebastopol, serving gourmet Mexican cuisine. 

A Yahoo Review:

"Hands down this is the best "Mexican" food in Sonoma county. The sauces are superb, Martha has wonderful touch with her seasonings. I have tried to order dishes that I do not consider to be my favorites, and I have yet to experience a poor meal. I have offered to run away with Martha on several occasions after eating her meals. She still thinks that I am joking. I am dead serious."