the Lewis Thrust ground over minor thrusts (made of soft Cretaceous shales) that would have formed foothills;
(the Lewis Thrust ground over minor thrusts; made; of soft Cretaceous shales) (the Lewis Thrust ground over minor thrusts; would have formed; foothills)
the Lewis Thrust ground over minor thrusts the Lewis Thrust ground over minor thrusts
made would have formed
of soft Cretaceous shales
foothills