The "Idlehour Descent" -- not really an idle descent at all -- is a one-way, 11-mile, mostly downhill hike through ever-changing terrain in the San Gabriel Mountains above Altadena and Pasadena. The name "Idlehour" comes from Idlehour Trail Camp, formerly a trail resort, passed at the midway point of the hike.
Have someone drop you off at Eaton Saddle, mile 2.4 on the road to Mount Wilson Observatory (2.4 miles uphill from Angeles Crest Highway). You'll end the hike at Eaton Canyon park, on Altadena Drive just north of New York Drive in Altadena.
From Eaton Saddle, follow the unpaved Mount Lowe Fire Road 0.5 mile west to Markham Saddle, where trails intersect left and right. Bear left on the narrow Mount Lowe Trail. At a trail junction (1.3 miles), the Mt. Lowe west trail comes in acutely from the right. Keep straight to remain on the shorter, better-maintained east-side route down along the flank of the mountain. At 2.1 miles you can either drop to the fire road on your right or stay on the trail another 0.2 mile to meet the same fire road farther south. Continue walking south on the fire road, curving left toward Inspiration Point as the road on the right descends toward Mount Lowe Trail Camp. After another 100 feet, turn left on the Idlehour Trail. You've now come 2.4 miles from the start.
On the narrow trail ahead, you descend through shade-giving groves of live oak and bigcone Douglas-firs. At 3.7 miles you cross a west fork of Eaton Canyon. You then climb a bit to cross a chaparral-covered divide to the east and begin a switchback descent into the main Eaton Canyon. Look for the faultlike discontinuity in the igneous rock exposed on Eaton Canyon's sheer east wall.
At the bottom of the zigzag descent (4.8 miles) the trail stays near the canyon bottom and becomes intermittently lost in a refreshingly cool wonderland of crystal-clear cascades, overarching oaks and maples, and crispy carpets of orange and brown leaf-litter. Cabin foundation ruins can be found under the trees, a reminder that even in this inviting hideaway, no construction is spared for long the ravages of fire and flood. After some easy boulder-hopping, you come to Idlehour Trail Camp (5.4 miles), nestled on an oak-shaded flat lying next to a rock fin, with vertical striations, dividing Eaton Canyon from its aforementioned west fork. This is perhaps the best spot for a picnic lunch.
Below Idlehour Camp, Eaton Canyon abruptly narrows, and its waters tumble over several near-vertical falls, 40 to 50 feet in height, in a three-mile stretch. Don't go that way! Continue on the Idlehour Trail, which ascends the left-side (east) canyon wall, then dives down to a junction with the Mount Wilson Toll Road (6.9 miles). Early in the 20th Century, telescope parts for the Mount Wilson Observatory were laboriously hauled up this road by mule-driven wagons. Today, the old toll road is reserved for self-propelled travelers. Go west, continuing your descent.
At 8.1 miles you reach Henninger Flats, which offers a small visitors' center, planted pines, and potable water. Continue descending to a hairpin turn (9.8 miles), where an equestrian trail takes off down the slope to the left. At the bottom, turn left and complete the remaining short distance to Eaton Canyon's nature center and parking lot.