Heaton Flat to Heaton Saddle is a 8.4 mile lightly trafficked out and back trail located near Azusa, California that features beautiful wild flowers and is rated as difficult. The trail is primarily used for hiking and is accessible from November until June.
A great hike if you're looking for a good workout, with fewer hikers along the way, and awesome mountain views from up high. My Garmin watch tracked it at 9 miles total (that includes the .5 miles from the parking to where the trail begins ascending). Took 4.5 hours to complete at a steady pace and with 30 minutes of resting.
I've done this trail 3 times, including the time I completed the strenuous Iron Mountain, of which this path is the "easy" first 4 miles of the 7 miles to the peak. I would still rate this as difficult and not a trail I would casually take someone new to hiking or that's not somewhat fit... for that, Bridge to Nowhere is what most people drive here for.
But if you're looking for an uphill challenge that rewards you with scenic feedback the higher you go, try this hike. Be aware that a good portion of the hike is along the ridge and therefore in direct sunlight. I've managed well with 2 liters of water on a cloudier Winter afternoon. Have fun!