This is a traditional ammo can cache.
You can access this cache by parking in the lot on the left, about a mile up Prefumo Canyon Road from Los Osos Valley Road, just past the first creek bridge, at 35 15.732 N, 120 42.711 W.
Head through the opening in the rail fence and up the Bog Thistle trail. It's about a 0.11 mile, 5 minute hike to the cache, but all UP.
After you find the cache, you can either return to the lot the way you came, or continue up the trail to the "T" intersection with another trail at another rail fence, and then turn left to return to the parking lot. As I recall, that is about a 45 minute loop.
Before leaving, check the weather for the Irish Hills Natural Reserve at SLOweather.com.
The initial cache contents were:
The logbook and pencil and disposable camera
Dogbone playing cards, magnetic notepad, #9 NASCAR toy car, ceramic teddy bear tree ornament, plush teddy bear tree ornament, 4" plush teddy bear, 2 bear resin figurine, 2 rubber grip SLOweather pens, one LED flashlight SLOweather pen, 3 WetNaps, 4 bandaids, and an 8 oz bottle of water.