This is a modified version of the classic Alpine dam loop ride.
From SF, we go to Fairfax and then on to the Dam. After the dam, we climb up the Fairfax-Bolinas Rd till we get to the Ridgecrest Blvd. Then instead of turning left and go up the 7-sisters, we turn right and descend down to Hwy 1. Then we take Hwy 1 south all the way pass Stinson Beach until we get to Mill Valley, then SF.
I don't have a route map at this time so am not sure of the distance and elevation. This is not a fast pace ride. However, since it has significant climbs and descents, it is not suitable for beginners. Also you should be able to ride with cars passing by you along Hwy 1. Do bring working lights that will allow you to see (and be seen).