The thing is in the West their's not alot o natural features you ca use without creating states that are either the size of New England States (which would have really small populations mostly) or really huge ones that'd be the size of Texas , if not larger.
In the East, well many states DO use natural features; the Missippi river forms large parts of the borders of 6 states, the Ohio 3, the Missouri river 2 and the Red river forms over half of Texas's northern border, likewise a good chunk of the Louisiana-Texas border is a lake (the sole natural lake in Texas) and the Mid-Atlantic states use the Appalachians as part of their borders.