The Irvine Ranch Wildlands is opening up the Northern Sphere area to the public to explore on Saturday. This area is not normally open to the public. In fact, this is the first time it will be open to explore to the public without being lead by a docent. There are tons of trails to explore in there. It connects up to Whiting Ranch if you have ever been in there.
It is free to go in there and parking is free too. Watch out for the mountain lions though. Truth is there is more potential danger driving there than you will have a problem with a mountian lion but they are out there in that park.
For more info
https://www.irvineranchlandreserve.org/activities/programs.asp?tid=0&aid=3630
If you take one trail you will see the mini-grand canyon of Orange County, CA
http://farm2.static.flickr.com/1073/1431099347_7809600cf0_o.jpg