Henry Coe State Park puts all other Bay Area parks to shame with its diversity of butt-kicking hikes. There's nothing remotely close. And it just keeps getting better!
Back in 1999, the Open Space Authority and The Nature Conservancy bought Lakeview Meadows Ranch. In 2001, Henry Coe acquired 2770 acres of that land for $1M. While the area is not yet maintained by the park--as you will find abundantly clear on the way there--they have started showing it on their maps. Good enough reason to check it out.
Technically this hike requires some planning, but there is already a string of caches along the way that will helpfully guide you there. I'd recommend doing some topographical and/or Google Earth recon before setting off.
With a park as large as Henry Coe, you really need big caches. This cache is big. And it's heavy. And high. And watery, too. If the route remains unmaintained, it's a hell of a hike. Oh, and you can see Coyote Reservoir's water from high up there. . .and the cache is precariously balanced high over a seasonal (?) water-filled hell hole. Everything about this cache is "high", "water", and "hell".
Please replace the cache similar to how you found it. Generally make sure it won't fall into the water. . .which you might not be able to see. . .just trust me.
If you like hiking as much as caching (or more!), be sure to visit all the caches in the Hardcore Hiker series. Here is a list of those who have found caches in the series. Are you hardcore?