Once you get to Valencia (Six Flags Magic Mountain) on the 5 take the 210 to Pasadena, Stay on the 210 for a long drive past the 15 then the 215 until the 210 merges with the 10. You could still get some significant traffic in the Santa Anita area. If you take this route there is a confusing merge where the left lanes head into Pasadena and exit the freeway and the right lane goes through an underpass to take you to onward on the 210. The far right lane goes to the 10. This all sounds confusing, but it is my favorite route from the San Fernando valley to points South or to Las Vegas by car. In the motorhome I take Palmdale highway to avoid the steep grade on the 15.