The Fullerton Loop is a complicated, unmarked route consisting of about 80% trails and 20% streets, shared with mountain bikers, horseback riders, and people walking their dogs.
Water is available from public drinking fountains at miles 3.5 and 10.2.
Running the loop counterclockwise gives you a better chance to see cyclists coming at you down the steep hills, since the cyclists usually go clockwise. If you take the shady singletrack on Hiltscher Park Trail
, visibility is poor, and you may need to yell a heads-up to oncoming cyclists.
From the parking lot behind the courthouse, head north and cross Harbor Boulevard to enter Brea Dam Park. Follow the Brea Dam Trail
to the tunnel that passes underneath Bastanchury Rd. and leads to the municipal golf course. Continue along the golf course to the top of a hill, and then descend to the railroad tracks. Go south 0.5 miles along the tracks to a bridge, and climb up the embankment to the Juanita Cooke Trail.
Go north on the trail to Laguna Lake. Run along the lake and take the Bud Turner Trail
to its end. Cross Euclid at the light and go 0.1 miles south to the start of the Nora Kuttner Trail
, which has separate entrances for pedestrians and cyclists. You now head up the tallest hill of the route, with the cactus fields and chaparral of North Coyote Hills on your right.
After coming down over the hill, use Castlewood Drive to connect to Castlewood Trail
, which takes you over two more hills, including the high-elevation point of the run. The trail now dumps you out near a fire station on Rosecrans Ave.
Follow a bike path east along Rosecrans, then leave the road to take a back trail that connects to West Coyote Hills Tree Park. Cross Parks Road and take Parks Road Trail
south through Gus Grissom Park, Roger Chaffee Park, and Edward White II Park, named after the three Apollo 1 astronauts who died in a fire on the launchpad. Head south along the railroad behind the high school's ag department, then cross Bastanchury at the light, go west a short block, and then east on Valley View Drive.
After 0.5 miles, Valley View ends, and you continue on trail down a steep hill where the Hiltscher Park Trail
follows a shaded gully. There is a wider trail on the left and a shadier singletrack on on the right. At the "T" intersection with a water fountain, head south on Juanita Cooke Trail back to the start.
The section running along Coyote Hills provides views of cactus and coastal sage scrub, which are a habitat for rabbits and coyotes. In spring, tall flowering mustard crowds in along this section of the trail. Laguna Lake draws ducks and sometimes other waterfowl such as coots, geese, and egrets.
West Coyote Hills was formerly an oil field owned by Chevron. There is a political controversy over plans to develop most of the land for housing.