New Years Day has two rides in the area. There are many online write-ups about them and even videos. Feel free to Google.
Mt. Wilson Ride
Shorter ride with lots of climbing. Large number of cyclists ride it, but at different times & paces. You make your own pace & turn around when you want. Mt. Wilson Observatory (5,700' elev) is the turn around point. Many local groups & clubs ride this.
Long Beach New Years Day Ride
70--100 miles. Very fast pace first 40 or so miles. Extremely large pack of riders (300+ usually). Many riders get to half-way point & turn around & come back--about 70-80 miles. Others turn inland & hit the hills, but get in 100 miles or close.
Based in Irvine, OCRR Team Tandems is a open group of Tandem Teams without walls in the So Cal area with teams from Channel Islands, Conejo Valley Cyclists, Redondo and San Diego biking clubs. Watch for updates and you are welcome to join in.