How far southwest over the Pacific would it have gone before turning back?
If it went far enough, it wouldn't have to turn!
The SID out of LAX going to, for instance, EGLL, generally depends upon the aircraft ability to climb. If you can go up fast, you can get the Loop (out to sea until you get to the point (or well past the point, some would argue!) where you can turn left and cross the LA VOR at or above 10,000 on your way toward Vegas). However, if you can't do that, you'll probably get the LAXX. It's almost like a Loop except that the turn is wider. Instead of going six or seven miles out over the water and cranking it back around toward the airport, you make a nice easy turn around Palos Verdes before heading northeast from the LA Harbor area. Note, however, that both are left turns.
If you saw the aircraft continuing off toward the southwest, then it was probably a LAXX. Loops tend to go out of sight pretty quickly (up into the haze) and then reappear overhead a few minutes later going northeast. Also, that guess of 30 degrees left wasn't bad... off the south complex the SID calls for a 220 heading.
The reasons for the turn to the left (south) instead of the right (north) are what have been mentioned... traffic and terrain. California has LOTS of north-south traffic north of LAX, and the terrain rises rapidly there. There ARE departures that go that way (obviously) over Ventura and Gorman, but if your'e a slow climber going north out of LAX with a right turn out, expect to see some ocean. You're going to go west for a while...
Dave
Edited to say saw United on the way to London get the loop, then five or ten minutes later, Virgin getting the loop, then five or ten minutes later, BA getting the LAXX. 50 miles later they were all on generally the same track.