I live in Southern California yet travel a lot and herp whenever I can. I've never spent any time in your area, however I'd expect to find Ringnecks and DeKays under debris and boards in open fields next to wooded areas. Ringnecks like artificial cover or rocks. The DeKays I've seen (Chicago area) were under artificial cover and tree bark. You typically won't see them out in the open. Same with the milks really. I've never found any of those out on the crawl. All of the ones I've seen (Kansas) were under rocks. Spring is the best flipping season, even if you don't get much of a winter. It stays releatively warm in Southern California, but the snakes still go underground until late February or early March. Don't look in heavily wooded areas. Not enough sunlight. Look around the open areas next to those areas. I believe some herpers follow train tracks through forested areas as they provide areas of open sunlight and there is debris along the tracks. Watch out for trains.
Look under stuff in the spring before it gets too hot. If it's too dry, that's not good either. A day or two after it rains seems to work best.
Maybe I'm telling you what you already know. I'm on YouTube at www.youtube.com/loub747
and post a lot of herping videos. The ones from Japan are typically "flipping" videos. Maybe they can help.
I look forward to hearing about your finds in the future.