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 you look around and see so many large trees it's often easy to forget that they weren't always so big.
ENJOY your surroundings.
You'll need tweezers and something to write with.