If you want to go to Wrightwood, go to the San Gabriel River trail to the north end (about 38 miles north of the beach) where it puts you on Hwy 39. That goes up to Hwy 2, and will be much shorter than going out to the La Cañada/Flintridge end of Hwy 2. The top half of 39 is closed to cars and supposedly bicycles too, but the forest service and rangers have treated us nicely and seem to be happy to see cyclists up there, knowing that they're enjoying the outdoors and doing something good and not vandalizing. Our son asked them for water once when they were working on the campground, and they even offered him lunch! Repairs are being made on the road and to the Crystal Lake campground for re-opening sometime in hopefully the near future. Crystal Lake is at about 5,000 feet. The top end of 39, where it meets Hwy 2, is at about 6,000 feet, and there's a gate there too. You'll go east on 2, and there will be another gate. The last time I was up there, it was closed too because that part of 2 is closed to cars, but I guess it's open now because the Tour of California race will be going through there. From the south end of the San Gabriel River trail to Wrightwood will be about 82 miles, and you'll get up to nearly 8,000 feet.
If you really want to start Hwy 2 in La Cañada/Flintridge, you can take the SGRT up a little over half way to Siphon Rd which is an east-west bike trail that splits off a few hundred feet north of Whittier Narrows Dam next to the Pico Rivera golf course, and go less that a mile (IIRC) to Rosemead, and take Rosemead north to Las Tunas in Temple City, and turn left (west). Go about about a mile, then turn north on San Gabriel Blvd., then after 3 or 4 miles, turn left (west) on Orange Grove Blvd. in Pasadena. Go about 3 miles and turn right (north) on North Fair Oaks Ave, go about 2 miles and turn left (west) on Woodbury Rd., and that curves north into Oak Grove Dr.. After passing the high school, turn northwest on Foothill, and in about a mile and a half you turn straight north and you're on Angeles Crest Hwy (Hwy 2). Caveat: I myself haven't ridden this way to get to Hwy 2. It's from my son's memory as he looked in the map book after I asked him.
Ok, he just Emailed me these links:
This is what he has done, but he's thinking that
this might be simpler. These both start where Siphon Rd. meets Durfee, right near Rosemead. He keeps meticulous records.
If you go by way of 39, you might go a long, long way, and do a ton of climbing, without finding any water or food (unless the forest service helps you), so take food and all the water you can carry. We put two one-quart (32-ounce!) Zefal Magnum water bottles on the frame and two more behind the seat, for a total of one gallon (128 ounces, much more than any Camelbak) to start, and refill at the little park a couple of miles before the end of the SGRT, and I still run out of water. I think I'll try to put another bottle or two in my huge seat bag next time. Hwy 2 has water at Mt. Wilson/Red Box Rd at a drinking fountain, and there's Grizzly Cafe farther up. Even farther up but before Cloudburst Summit (IIRC) is a campground on the left side of the road. It seems like there would have to be water there, but I don't know/remember.