The Davis Bike Club puts on the Davis Double, which is one of the most highly regarded organized rides on the west coast.

http://davisbikeclub.org/

http://www.sacwheelmen.org/

I'm from Sacramento and recently moved back to NYC after living there for a year and a half. There are two well-known bike clubs, the Sacramento Wheelmen and the Bike Hikers. The Wheelmen are very FAST and they do not usually sweep on their rides. These are serious riders and in my best shape I had trouble keeping up with them (and I had age on my side!). The Bike Hikers are more recreational and less organized. There is also a women's bike club, Ophir Milan and I did some rides with them. Email me if you want more info. The best thing about that area is its FLAT and the American River bike path can take you (for the most part) from Davis up to Folsom Lake.