Mtbiking near Newport Beach/Costa Mesa area in California?

Anybody have any experience or tips for some good mtbike trails in the Newport/Laguna Beach area in California. I am going to be out in Costa Mesa, CA the last week of April on business and will have some time to hit some local trails. Looking for anything within an hour or two of Costa Mesa.

Any recommendations on trails and Local Bike Shops where I could rent a bike would be helpful!

Thanks,
Derrick