Call or stop by and talk to Roger at Newhall Bike Co. 661-284-6187 They do a Wed. night ride @ 6ish, not sure where they are going this week though. Great bunch of people that ride with the NBC crew. Also check http://www.clipdin.com/ a lot of SCV riders on here.
Check out "teamkarma.50megs.com" I live in Granada Hills and have met up with them at Hummingbird Trail at Rocky Peak and have been riding with them for 3 months now. Most of the guys live in the valley and we have regular Sunday morning rides on the different trails of Sta.Monica & San Bernardino.
The group consist of x-country riders & all mountain/light free-ride rider ( which I am one of ). Just last Sunday we rode down at Viper trail right by the 5 & 14 freeway! Check out the website, show up & lets ride!