Divisadero is a combination of beautiful woodsy singletrack and tough rocky terrain. At .7 miles, the loops begins. To the left is a wooded singletrack ascent and to the right is a tough, rocky climb. Both directions are possible, but most people seem to go to the left here at the beginning of the loop. That way, you can come down the exciting rocky bits on the way down. :)
From the El Nogal parking area (which is on US64, .5 miles east of the intersection with NM585) cross Rte. 64 and you will see the trailhead, easily marked.
http://www.singletracks.com/item.php?c=1&i=5938