Briones Regional Park
Getting There.
Briones is located in the East Bay, in the middle of Contra Costa County, located between the cities of Lafayette, Walnut Creek, Pleasant Hill, Concord, and Martinez.
There are 5 entrances to Briones.
You can view more information from the official site.
Briones is the red outlined green blob on the right.
Here is its location realtive to the surrounding towns. I live in Pleasant Hill.
Here is an overview map of the park. You can also grab the high res PDF map.
Here are some additional links.
http://www.bahiker.com/eastbayhikes/briones.html
http://www.coloniapress.com/hikes_trips.html
http://www.mtbreview.com/trails/California-BayArea/BrionesStatePark.html