Sibley Volcanic Regional Preserve

You can choose any of the handful of trails; Round Top is one of the most popular.  The trail head starts just a stones throw from the parking lot and its a  rollercoaster of trail.  You start low, walk through a very lush forest, climb a little into more expansive green landscape, dip a little and continue on until it opens up entirely to hills of dead grass and hay calf-high.  There are also parts of this section that you share with cows lazily grazing and laying about.  Then, you drop a little more until you're back amongst the trees.  Did I forget that the highest part of the hike, Round Top, is entirely beautiful, opens to gorgeous scenic views of the surrounding landscape of Oakland/Temescal, and is very windy, but worthwhile.  You can walk further out and see the strange rock mazes.

There are lots of trail runners and mountain bikers, so make sure your unleashed dog is at least in ear shot to be called back, and that you're sharing the trail.  It's also a large enough regional park that you could visit a handful of times and get a different hike out of it each time.  Have fun, stay hydrated, and enjoy the sights/sites!