Dear M Ashley: The choices in California are vastly different than Illinois. A non deciduous could be a needle evergreen or a broad leaved evergreen. It would be best to contact your local Extension Office for specific recommendations. You could also visit a retail garden center or nursery and see samples.
Once you make your choice, consider how wide the plants will grow (besides the height requirement). the more space you allow between, allows those plants to grow to their full potential without crowding out the lower limbs, leaving them full to the bottom and provideing the screening you desire. The closer you plant them the sooner they fill in, yet the sooner they will begin to thin out from being planted too close together.
Sincerely, Richard Hentschel