This is the east side of Perimeter Trail as it crosses the north side of Los Alamos. It starts at the intersection of Mitchell Trail and West Perimeter Trail above the parking lot on Arizona St. The trail descends downhill to the east and crosses several residential streets before climbing around the cemetery and up to the roundabout on San Ildefonso St.
From there, you can take several different trails in three different directions to extend the ride. Across the street is Walnut Canyon Trail that returns back up to Perimeter Trail.