This is what I usually do, you may want to take the 57 to the 10 instead of the 15.
From OC, take the 91 East. Get on the 15 North. Take the 10 West. Exit on Mountain and take a right. Stay on Mountian for as far as it goes. It gets a little confusing when you are on the outskirts of Upland. The road will curve right and then back to the left to a stop sign. Take a left to stay on Mountain. Mountain then joins with and becomes Mt. Baldy Road. This will take you through the village of Mt. Baldy. The ranger station is located here. You will need to get a parking permit for Angeles Crest Forest. Continue up Mount Baldy Road. Got pat the village and when the road makes a turn to the right, go straight into Icehouse Canyon. You will hit the parking area immediately. The trailhead is where the road ends.

For other information, you can call the Mt. Baldy visitor's center at (909) 982-2829.