This cache is part of the 100-Mile Hike series. The cache is hidden in Joseph D. Grant County Park, or Grant Ranch, in a huge meadow that I assume is "Dutch Flat." I'm only guessing about Dutch Flat, since I arrived there after hiking all the way to the far point of the Dutch Flat Trail. But it is flat! And very large.
You're looking for a small ammo can hidden in a straightforward manner. It's in the middle of a huge field, with few possibilities once you get there, so it should be easy to find. Although the location looks like it's far off the trail, there's actually an unmarked, single-track trail branching off the Canada de Pala Trail that takes you most of the way there. It is well within the park boundaries.
This cache will add a minimum of 4.4 miles to your "100-Mile Hike" tally if you go straight there and back from the main parking lot. But I highly recommend any loop that includes the Dutch Flat Trail, for its amazing panoramic views of the valley. Any loop in the lower part of the park that includes the Dutch Flat Trail and this cache will be in the 7 - 9 mile range. Make sure to note the keyword for the 100-Mile Hike final. It's in the logbook and on the lid of the cache container.
Joseph D. Grant hours are 8:00am to sunset. Unfortunately, parking is limited outside of the parking lots, so you'll have to show a county parks pass or pay the fee. Happy hunting!