From the Devore Road crossing to Blue Cut, Swarthout Canyon and Cajon Station/Sullivan's Curve, up through Pine Lodge, then crossing back under the I-15 and on to Alray, the Tunnels, and Powerline road. With the tracks last swing southeast the Summit is just ahead to the east (where State Hwy 138 comes close to the tracks) and then out of the Pass through Summit Valley where the U.P (old S.P.) tracks heads northwest towards Palmdale and the Burlington SF (old ATSF) tracks head to Victorville.
Cajon's Devore is the most consistent viewing area, where you'll find rail fans any time of the day and all 3 tracks come close together.
Traveling north, up the Cajon Pass on the old Cajon Blvd will bring you to Cajon's Blue Cut and Swarthout Canyon areas.
Cajon Station and Sullivan's Curve are next as you go north on Cajon Blvd.
Return to I-15 north, and get off at Hwy 138 and travel west to see Cajon's Pine Lodge area. Also from Hwy 138 and exiting on Lone Pine Road, Sullivan's Curve is more closely accessible. Alray can also be reached by exiting the I-15 at Hwy 138. At the top of the intersection of the off ramp and Hwy 138, look straight ahead and take the dirt road that parallels the onramp to the I-15 north (it hugs a hill).
Backtrack to Hwy 138 and go east to Cajon's Power Line Road area. This favorite viewing area has long sweeps of canyon, where all 3 tracks can be simultaneously be seen.
Once the broad Cajon canyon is traversed, Santa Fe's Summit / SP's Hiland is not far ahead on Hwy 138.
The San Timeteo Canyon's Signal Bridges are some of the last of their kind in the area.
Santa Susana Pass is noted for it's unusual rock formations. After the Coast line leaves the shoreline, it comes through the Santa Clarita and Simi Valleys and then onto Chatsworth, passing through this wonderfully scenic area and the restored Simi Valley Station.
Last of the rail side viewing, but certainly not least favorite, is the famed Tehachapi Loop. Noted as being a great engineering fete, this is certainly the highlight of a rail fan's trip to the Tehachapis. But there's a lot more to see. The whole Tehachapi area is a worthwhile trip.
The San Diego Railroad Museum's most eastern facility, at Campo, is an experience for those wanting to ride on a steam train. In fact, here, you can actually ride in the cab of the restored 1912 Baldwin #2353 for a price.