Visiting Turnbull Canyon is a site to see in the spring, and taking the Sycamore Canyon Trail up allows for some beautiful view of the valley and Downtown LA.
The Sycamore Canyon Park Trailhead can be found at the end of the dirt parking lot off Workman Mill Road. The entrance is off a small road which is pretty easy to miss, but there is a sign off the main road. Soon after you start on the trail, the path opens up onto a larger dirt road for vehicle access, but it is only accessible for city vehicles so there shouldn't be any disturbances. After a short while, the trail picks back up on the opposite side of the road. Follow the trail along until there is a fork in the path and you see the sign to continue on Sycamore Trail or Dark Canyon Trail. This is around 1.3 miles along the trail. Take the trail to the right, which begins with a small creek crossing and then starts the up hill climb. You will continue on the switchback portion of the trail for 0.6 mile before making it to the top of the canyon. Right before you reach the top, on a clear day, you can see Downtown Los Angeles. (You can also get some great views of Downtown LA at the top of the trail taking an immediate right heading towards the large water tower).
Once you make it to the top you can explore the top of Turnbull Canyon and check out other trails with the park. Spring might be the best time of year to hike this trail due to the amount of yellow wild flowers that are in bloom.