Exit Chapman (L)
Take Chapman all the way into the hills (it turns into Santiago Canyon Road). A couple miles past Irvine Lake you'll see some signs for Silverado and Blackstar Canyons on your left. Make a left onto Silverado Canyon Rd and take it all the way up (4-5 miles) until it dead ends at the park entrance.
I usually exit Katella instead of Chapman but that requires me to type more directions and I'm lazy right now. I'd give you a ride since I live in Fullerton, but I'm going somewhere in south county right after the ride.
Seems like it's gonna rain tomorrow. Those who want to ride can ride at Motorway/Blackstar as Maple Springs has a small danger spot which is ready to slide soon.