Why do you want to avoid high mountains? What is high for you? Some people have problems with altitude. Others are concerned about grades - up or down. Or maybe it's the potential for snow.
On I40 there's a grade where it drops from the high plains level to the Rio Grande at Alb. It then climbs gradually to Grants and the Continental Divide. Flagstaff is another high area, known more for snow than grades. Then a drop to the Colorago River west of Kingman.
CA 58, Tahachapi Pass takes you from the California desert into the Central Valley. I15 Cajon Pass is the major route from I40 to the LA basic. I5 Grapevine the main route north out of the basin. I10 from Palm Springs is a lower pass. All of these are busy freeways. Grapevine may be most notorious for grades (mainly downhill north bound) and occasional weather problems.
Then there's the question of when you want to cross over to 101, whether you take it all the way from LA, use something like 46 to cross from the Central Valley, or wait to I580.