The Boulders of Sisyphus series of caches highlight a number of repeating hiking outings that seem almost Sisyphean in nature. At first blush, Ground Hog Day may appear a more appropriate name, but there is also a back story to this series (left for another day or interpretation of an occasional log entry or two).
The hike to Henninger Flats is a very accessible and crowded fire road from Eaton Canyon. It is a steady 3 mile hike (one way) on a south facing slope, so it can get uncomfortably hot even during milder months. Once at Henninger Flats, there is an abundance of shade and pine trees to relax and cool down while taking in the sights of the LA Basin (if you catch it on a clear day). The more adventurous can haul some camping gear up here and spend the night at one of the many sites in the area. It appears they even supply the fire wood, although fires are restricted to the site's iron stove. If camping is your goal, make sure you get better info than this scant amount.
There also seems to be an adequate source of potable water for public consumption, although I have been there when that was not the case. Regardless, besides checking the conditions before hand, you should always travel with plenty of water.
In my many trips up this trail, I have never seen a rattler, but there are signs at the camp sites, and I have run into folks who had seen one along the road. Play it safe and watch where you poke and prod.
The cache is a camo-ed pint size gelato container. It is towards the far end of Henninger Flats, but you may still need to watch out for the occasional muggle.