Best route is east of the San Gabriels. As you go north on 15 through Cajon Pass, look to the NW, up Lone Pine Canton toward Wrightwood, and know you are looking at the San Andreas Fault, as you pass from the Pacific plate onto the North American plate. If you have the time drive through Phelan, not that there is much to Phelan, but as you come over the rim from the pass on 138 onto Sheep Creek Rd, and the expanse of Antelope Valley opens up, you will see El Mirage Dry Lake off to the north. From this perspective it will appear as a light thin strip in front of the far mountain range.
Yes, I am a Geologist.