This is a great overview day-run of one of the best East Bay parks, Sunol Wilderness. It hits several of the park's highlights and traverses two halves of the park that have distinct personalities.
I recommend this run in the spring, when the hills are verdant and temps are manageable, but summer/fall is doable with proper hydration/sun protection and winter with an extra layer.
$5 entry to Sunol. Bring lots of water, food, sun protection (obviously). Footwear: trail runners if dry, boots if wet.
Great trail run if you don't mind a couple of very steep sections. I've met several trail runners in Sunol. If you're looking for something flatter, the road past Little Yosemite may fit the bill.
I did this route clockwise but it would likely be just as good either direction. Clockwise, there's a very steep gain right away (~1k) and the rest of the run is quite manageable. Counterclockwise, the initial gain is more gradual but longer and tops out higher.
There are two options for shortening this route. You could cut out the "loop" section of Flag Hill, or you could cut out Little Yosemite and take Canyon View Trail
back to the visitor center. To cut this route roughly in half from either direction, you could take Indian Joe Trail back to the visitor center. To lengthen it, you could add Grande Vista, or, to really make it a monster, add the Maguire Peak Loop Trail
Terrain varies from wide gravel road accessible to strollers (parking lot to Little Yosemite) to very steep singletrack trail (Flag Hill area). All of it is well-maintained.
I did run into several small herds of cows, some of them blocking the trail. For those of you who don't have experience with cattle, just proceed confidently and assertively and walk around if they're in the trail. They're harmless. (This does not apply to bulls, which were not present.)
Highlights of this run:
1. Flag Hill, a prominent rock outcropping overlooking and visible from the valley. The Flag Hill loop circles around this area. The section that loses and regains elevation could be skipped to make this run a bit easier.
2. High Valley Camp area is very picturesque and wide-open. There's a barn and a camp area here, and I'm not quite sure what the use regs are (entrance was blocked off).
3. Cerro Este, the high point of the run with views in many directions.
4. Little Yosemite, where you'll reunite with the masses. This is a popular day-trip area for families and groups, a rapids section of the river with granite rockfalls.
The plotted map starts at my parking spot. If you're going clockwise, start at the footbridge near the visitor center. For counterclockwise, start at the trailhead for Little Yosemite.
Lots of ground squirrels. Red-headed woodpecker, turkey vultures, Cali jays. Newts. Lots of cows. Beautiful gnarly oaks.