i rode the santa ana trail during the smog to surf... but it wasn't straight out and back.. there were a few places you had to go roundabout and up and over ! if it hadn't been marked for STS i surely woulda gotten lost! then the bridges!

however... it is FLAT as a pancake so very fast... as long as you know where you are going it's a fast mileage builder!!!

don't know anything about san gabriel!

hopefully some others have some info for you!