Basically it's 8 mile climb to the top of Mount Tam and a great downhill back to Ross. The views are great and altough it's all on fire roads it's a pretty cool loop.
Riding by Lake Lagunitas and Lake Bom Tempe is a bonus!
Start at Ross Common. Parking in front of post office.
http://www.singletracks.com/item.php?c=1&i=1116