The Quarry Road Trail in Auburn State Recreation Area is a 13.5 mile out-and-back hike that actually follows a portion of the Western States Trail.
It’s a wide dirt path that is perfect for trail running, easy mountain biking or hiking. It’s also dog and horse friendly. Follow the American Canyon Trail another mile to some small waterfalls and a deep little hidden pool.
For more details, check out the Norcalhiker Blog post for this trail.