Been to Dirt Mulholland, its not bad for a mile or so, then a straight drop for like a mile, rough on the way back. Didn't get to ride far as I got a flat and had some trouble with my co2 pump and an old patch kit, didnt really get a good inflation after the patch job and I was then fresh out of patches. Got a new patch kit and looking into a frame pump now to solve that issue. You are the second to tell me that trail is pretty flat, maybe I rode down the only crazy hill on the trail, I'll try it again.
As for the single speed thing I am trying to build up my endurance for single speed cross before next season, but I like the off-road stuff a lot. When I get more room to store bikes I'll get a dedicated mountain bike, but these LA apartments aren't very big. In the mean time I just want to find some fun fast off-road stuff.