Park-like Henninger Flats is a cool "sky island" in the front range of the San Gabriel Mountains, just behind and above the cities of Pasadena and Altadena. The flats and slopes hereabouts have been the site of an experimental forest for more than 70 years, with seedlings of pine, cypress, cedar, and other trees raised for reforestation projects. Run by the Los Angeles County Fire Department, the area includes camping and picnicking areas, a visitors' center, a pioneer museum, a short nature trail, and a seedling nursery. The visitors' center features a large relief model of the surrounding mountains, including nearby Mount Wilson, the summit made famous by its historic astronomical observatory.
Getting there, by way of the historic Mount Wilson Toll Road, requires self-propelled means and some determination. The old toll road -- now a fire road used by fire-department or forestry trucks and a steady stream of hikers, runners, and mountain bikers -- starts at 2260 Pinecrest Drive, 0.5 mile east of Allen Avenue and Altadena Drive. Walk through a gate, which generally stays open between sunrise and one hour after sunset, and then down to a narrow concrete bridge over Eaton Canyon. Dogged determination, and hopefully the inspiration of fabulous views over the big city below, will get you up the moderately steep and steady grade ahead, some 2 miles of walking with an elevation gain of about 1500 feet. This well-engineered road/former trail was built and improved primarily to haul telescope parts to the summit of Mount Wilson, including those of the 100-inch Hooker Reflector -- the world's largest telescope for 31 years.
You can easily use up a couple of extra hours at Henninger Flats poking around the museum and the visitors' center and taking short side trips to check out the groves of trees. For the best view of the surroundings, try climbing a little higher to Henninger Ridge: continue upward on Mt. Wilson Toll Road another 0.6 mile, and turn left on the dirt road that loops around to a heliport. This puts you on the shoulder of a ridge perched 400 feet above the groves of Henninger Flats, where the view of the city below stretches 180 degrees. From the north side of that ridge, Mount Wilson rears up starkly, less than 3 miles away. After a winter storm, the spike-shaped television antennas on its crest look exactly like upside-down icicles.