It's not easy, but here are a couple of possibilities. You could try the Folsom Stage Lines commuter bus
http://www.folsom.ca...ex.asp?page=160 to Sacramento and then walk or take RT to the Amtrak station in Sacramento and take Amtrak to Davis. Folsom Stage Lines also runs a bus to the Butterfield light rail station, although I would call them because that bus might go to Sunrise now and all of their busu routes are changing on October 15th when light rail opens.
Alternately, you could drive or bike to the Sunrise RT station and take light rail to Sacramento and Amtrak to Davis.
Yolo County Transit also runs buses from Sacramento to Davis.
http://www.yolobus.com/m3.htmlIf you are traveling after October 15th you will be able to take light rail directly from Folsom to the Amtrak station in Sacramento (at least I think thae Amtrak extension will also be openening on the 15th).
El Dorado Transit
http://www.eldoradot....com/routes.htm also runs commuter buses into Sacramento from the El DOrado Hills Park and Ride Lot.
Currently, none of these options provides particularly good service from Folsom, but it will improve with the light rail connection in October. Hope this helps a little.