As a tree ages, it may become subject to various natural forces - such as wind, storms, lightning, fire, rain, bacteria, fungi, etc - that can cause hollows or cavities in their trunks and branches. It's amazing what a tree can survive!
After passing this particularly curious tree many times, I thought it might provide an interesting spot for a cache. If you are driving up Partrick Road from downtown Napa, or the Browns Valley area, it is safest to drive past the tree, and turn around about a quarter mile up the hill at the entrance of a winery. Then, head back down the hill, grab the cache, and go back towards town.
This area of Partrick Road is known for being part of the Mount Veeder Appelation, and for its legendary mythical "rebobs." (Ask an old-time Napa native about them, if you are curious!)