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
Although this is not technically part of the Blue Trail, it is easily accessible as you make your rounds. In fact the trail can be reached from Conover Rd here, but parking is not ideal. OK.....who am I kidding.....I just wanted to get one more cache in.
ENJOY!
Don't forget your tweezers and whatever you're writing with.