The Blue trail is easily accessible, is great for hiking/biking, and has some great views across the lake.
Here are links to the official park site & to a trail map:
http://www.mercercountyparks.org/parks/mercer-county-park
http://www.jorba.org/sites/default/files/2010_SMART_trail_map_0.jpg
When I first started placing the MCP BLUE TRAIL caches, it had recently rained and this whole area was flooded. As a result cache 25(a) was born. Well, I waited for some dry weather to return and complete the Blue Loop (actually this might be part of the Red Trail, but don't tell anyone). If the water reaches this one, I might have to turn it into a kayak cache.
Hope you didn't lose that pen. (I think I lost a couple as I was placing these)
ENJOY!