A short steep canyon cut through the front range of the San Gabriel Mountains directly above town, with a seasonal creek, several small waterfalls, and pools that fill in spring. The hike up the canyon from the trailhead at Sapphire Street is unmarked, scrambly, and locally known as "Sapphire Falls" — popular with teenagers in summer and prone to overcrowding.
Parking is limited and the access is through residential streets; respect signage and the no-parking restrictions. The trail crosses private and Forest Service land and the legal status of public access fluctuates — check current conditions before going. Better-marked trails are accessible from the Cucamonga Wilderness trailhead farther east, off Mount Baldy Road.