 During the growth of the Rocky Mountains, the angle of the subducting plate may have been significantly flattened, moving the focus of melting and mountain building much farther inland than is normally expected.It is postulated that the shallow angle of the subducting plate greatly increased the friction and other interactions with the thick continental mass above it.Tremendous thrusts piled sheets of crust on top of each other, building the extraordinarily broad, high Rocky Mountain range.