From South Dakota and Nebraska northward far into Canada and westward to the Rocky Mountains there extends an ancient peneplain worn down to gentle relief by the erosion of millions of years.
(there; extends; an ancient peneplain worn down to gentle relief by the erosion of millions of years) (an ancient peneplain; worn down; by the erosion of millions of years)
there an ancient peneplain
extends worn down
an ancient peneplain worn down to gentle relief by the erosion of millions of years
by the erosion of millions of years