Buckhorn Falls are located at first fork in the trail to your right (a slight detour downhill and off main trail) and Cooper Canyon Falls are located at the bottom of the canyon near yet another fork in the (The trail is not easy to spot the first time) trail. Veer right at the fork and look to your left and you will see the falls. Look for a trail that veers steeply downhill to the left. You will know you are at the right spot because you must climb down a rope. If you continue on the main trail and reach the creek you went to far.
This trailhead is located within the Buckhorn campground which is about 30 miles north of La Canada Flintridge via Highway 2. At the time of this writing the Buckhart trail is open but access through Buckhorn campground is prohibited. I didn't really see this being enforced but several tiny signs inform people that Buckhorn campground is off limits. Parking however was strictly enforced and an Adventure Pass is required. Remember to punch a hole in the appropriate month (the month that you purchased your pass) on the pass. One car was ticketed for not having a pass because they did not punch a hole in the pass.
Signs within the area suggest visitors park at Cloudburst summit parking area or Eagles roost parking area to access the falls. The signs are visible but tough to spot. I would suggest purchasing a map of the area as many trailheads are not clearly marked. One downside is that approaching the falls via Cloudburst or Eagles roost turns a moderate 3 mile hike with 700 foot elevation gain (Buckhart trail) into a more difficult hike of 7 miles with a over 1700 foot elevation gain (Cloudburst).
Whatever route you choose try to follow the many confusing rules of the forest. See below for more details on this hike:
Cooper Canyon Falls via Cloudbuurst (7 miles)
Cooper Canyon Falls and Buckhorn Falls via Buckhart trail (3 miles)