This is an extremely popular paved pathway around Lafayette Reservoir. Plan on seeing lots of dogs, joggers and strollers.
Lafayette Reservoir was created in 1933 to be an emergency drinking water supply for EBMUD (East Bay Municipal Utility District, or "Eee Bee Mud") with this trail as a side benefit. The higher Rim Trail is more interesting and challenging, but the lakeside setting for this trail makes it a great place to stretch one's legs.
The hike starts on the dam which is on the north side of the reservoir near Mount Diablo Boulevard, and is a loop around the reservoir. Going counterclockwise takes you past the fish-cleaning station towards the small visitor center and boat rental center. A series of small picnic areas are on the left (towards the lake) before the route gets pretty wild for about a mile. It's not a federal wilderness area by any stretch of the imagination, but there are decent-sized stretches where it felt like I was 'out there.'
The route continues around the lakeshore through a mix of valley oaks, Monterey pine, tan oak, bay, willow and non-native eucalyptus before passing some large group picnic areas just before reaching the parking area on the dam.
Check out the Official Route.