Turtle Creek? Hmmm There is a Turtle Ridge housing community above the 405 in Irvine.
If you're leaving HB head south on PCH which will take you through Newport beach, past fashion Island on your left then through Carona Del Mar (Which I think is still the city of NB) then about 3 miles past Carona Del Mar is the entrance to Newport Coast. Newport coast is a pretty high end area with expensive homes. At the top of Newport coast hang a left past the shopping center and it will take you back down the hill to Fashion Island and PCH. If you do two rides you will want to go past Newport coast and head down to Laguna Beach.
Depending on the speed and difficulty you are looking for, there are some great group rides nearby. There the OC riders. There's Bicycle Club of Irvine (http://www.bikeirvine.org/). And for a fast group, Team Velocity in Fullerton (www.teamvelocity.org). They have great hills on every ride. I promise you will not be disappointed.
The group is separating which makes it insanely more difficult to draft. coming thought the final turn, I stood up and laid in the acceleration, sprinting. One guy next to me was doing the same, and he was just a hair faster than I, but he couldn't hold it for the duration and I edged out in front. I passed two other riders who had were not sprinting. It doesn't really mean anything since I am no where near the top 20 among this 105 riders present. Yeah, there was quite the turnout for the first race of the season. End result, I am happy with my performance today. And as I said earlier, I still have all my skin.