Road up to Oak Glen is moderately difficult. You go from about 2,000 feet to just over 6,000 feet in elevation. From Yucaipa, you would have to ride over to Beaumont then start your climb. Parts of the ride averages over 6% grade. You will need a SAG to give you some water on the way up. the weather is already getting pretty warm and dry up there. So unless you have two water bottle cages on the frame and additional two bottle cages on the back of your seat, I think it would be a stretch to ride up to Oak Glen without a SAG.
If you are living in Palos Veredes Peninsula I can suggest several routes for training. Please PM me and we can talk where you might want to ride and how long. Big loop, or shorter loop with hard hill climb, or just down the coast line..
Check your PM and look for my phone number and we can talk.
sincerely,
Shawn