Almaden Quicksilver County Park is nice place to go for a short, non-technical mountain bike ride. Wide fire access roads without much rocks or gravel make the riding pretty easy. The loop that I like starts with a steady uphill climb to the ridge top. The climb is followed by a fun downhill ride to the reservoir and then finishes off with a mixed up and down section. You could of course do the same in reverse but I like to get the big hill climb out of the way first. I almost ran over a big snake that was sitting in the middle of the road so be careful.
See this ride on Everytrail