The Pleasanton Ridge Trail is a great Bay Area day trip, located in Sunol. The trail features wildflowers and scenic views.
Pleasanton Ridge Trail is a 6.4 mile loop. The loop is shared by dog walkers, trail runners, hikers, mountain bikers and horseback riders. From the ridge your viewpoints will include Mount Diablo and the San Francisco Bay.
This hike from the Foothills Staging Area is an excellent introduction to the park: long enough to get your heart rate up, but not nearly as arduous as some hikes in the nearby hills.
Water spigots are available to refill your water - but bring extra just in case. The trail also passes through a grove of olive trees from a previous ranch.