My friends and I hid this cache while doing the following loop in Anthony Chabot Regional Park:
Brandon Trail > Towhee Trail > Honker Bay Trail > Columbine Trail > Two Rocks Trail > Brandon Trail.
The closest loop on AllTrails: https://www.alltrails.com/explore/trail/us/california/live-oak-honker-bay-columbine-brandon-trail
We just recently discovered geocaching in the South Bay, really enjoyed the experience, and decided to make our own treasure chest 
Right along the northern side of the Columbine Trail, you will see a tree with multiple trunks. The cache is hidden in its roots.
Stay safe and have a great hike!