UPDATE 24-SEP-2018: Thanks to the efforts of the Mount Wilson Bicycling Association, the Gabrielino Trail between Switzers Trail Camp and the Arroyo Seco has been restored, and is now open to the public.
The Gabrielino / Arroyo Seco loop is one of the hardest rides in the Front Range. Doing this ride as a loop is an arduous day-long adventure for most, and the technical difficulties range from rocky stream crossings to narrow cliff-hanging trail with loose surface.
There are a few options for reaching the top of the trail, easiest of which is a car shuttle between Jet Propulsion Labs in Pasadena and Red Box Station, where the Gabrielino Trail starts. For those choosing to earn your turns, there are a few climbing routes that get there. Easiest of these is riding Angeles Crest Highway, though this road has a lot of traffic and can be dangerous. Not as easy as the highway, but much more scenic and safe, is climbing up the Mount Lowe Railway. The Sam Merrill Trail provides a singletrack option to the paved start of the Railway route. The most difficult non-trail route is the Mount Wilson Toll Road...11 miles of nearly constant climbing!
Though the whole loop is covered on this page, the 'downhill' portion can be broken into sections. The most popular section is the upper part of the Gabrielino Trail from Red Box to Switzer's. This section is often done in combination with the nearby Strawberry Peak loop. This upper section, while having it's share of technical terrain, is moderate compared to the lower section between Switzer's and the Arroyo Seco. The Arroyo Seco section down to Jet Propulsion Labs has many stream crossings that usually must be walked, but is generally a nice cruise through the canyon bottom.
The Gabrielino Trail starts at Red Box Station, where the Mount Wilson Road leaves Angeles Crest Highway (CA-2). The trail follows the upper canyon of the Arroyo Seco down to a point just below Switzer's Falls, then crosses over into a small side canyon, then regains the main canyon at another waterfall. From here, the trail generally stays in the canyon bottom, except for a switchbacking climb above a debris dam at Paul Little Picnic Area.
Red Box to Switzer's Picnic Area
The trail starts at the northwest corner of the parking area at Red Box. Dense forest of oak and pine shade the first traverse across some side canyons, then switchbacks lead down to the canyon bottom, where the trail plunges through a nasty rock-strewn chute. Things get a little more fun as the trail meanders around the creek bed and occasionally climbs over debris dams. At the upper end of Switzer's either the now-paved trail or the road can be used. Continue through the picnic area and pick up the paved trail on the other side.
Switzer's Picnic Area to Bear Canyon Trail
From Switzer's the trail is paved, but deteriorating. Dodge hikers and occasionally dismount to cross the creek or boulder-hop. Just before entering Switzer's Camp (a trail camp separate from the picnic area), cross the creek at a small sign and climb steeply out of the canyon bottom. The trail levels off and traverses across some cliffs, and the impressive Switzer's Falls can be seen down in the canyon. Veer right at the Bear Canyon Trail junction, and continue traversing around the mountain.
Bear Canyon Trail to Arroyo Seco
Around the mountainside the trail drops into a beautiful side canyon. At first the going is a bit tricky, dipping back and forth across the creek. Then the roller coaster begins. Swoops and curves on nearly perfect packed duff lead down the canyon, through alder and maple that turn brilliant colors in autumn. The trail hugs the cliff 25 to 50 feet above the creek, and there are a few tight spots where the cliff can snag the handlebars. This small side canyon dumps into the Arroyo Seco over a high waterfall. Dismount and cross the creek right above the fall and then drop into the main canyon for the duration.
Arroyo Seco to Paul Little Picnic Area
This section is more sugar. There is more roller coaster, then the trail drops to the creek bed and fast straights with some curves lead into Oakwilde Trail Camp. There are tables here on the foundation of an old mountain resort. The trail goes over a broad set of concrete steps before crossing the creek and continuing through increasingly gravelly terrain. Cross the creek at a wide but shallow spot and head into the forest to climb some steep switchbacks. At the top of the switchbacks the trail traverses a high cliff, where chain-link fence guards the 'downhill' side. There is a huge debris dam here, far below in the canyon, forming a high artificial waterfall. The trail now drops down some rough switchbacks into Paul Little Picnic Area. Go left and continue down-canyon.
Paul Little Picnic Area to Jet Propulsion Labs
The trail gets easier, except for the occasional rocky stream crossings. More traffic is encountered as the trail turns to road. Pass the Ken Burton Trail on the left (east) and continue down past the Jet Propulsion Laboratory, where the road ends at a public parking area at the corner of Windsor Ave. and Ventura St. in Alta Dena.
Getting ThereFor riding the trail as a loop, or for the lower end of a shuttle, the best parking is at the Jet Propulsion Labs entrance gate on Windsor Ave. Exit the I-210 Freeway at Windsor Ave. in Pasadena and go north to Ventura St. There is a parking area on the left where there will usually be many bicyclists gearing up.
For riding as a loop, leave this parking area and ride east on Ventura St. to Lincoln Ave. and go left, heading north to Loma Alta Dr. Go right on Loma Alta Dr. and climb up to either Cheney Trail (for Mount Lowe Railway option) or continue to Lake Ave. (for Sam Merrill Trail option).
For riding as a shuttle, drive the 'second' vehicle back to the I-210 and go west to Highway CA-2 (Angeles Crest Highway) and exit. Go right and head north into the mountains. Continue 9 miles to Red Box Ranger Station and park here. This is the upper terminus of the trail.