The great monoclinal fold which formed the eastern face of the east Australian highlands, west of Sydney, is of later age.
West of the Columbia river the plain is broken by several monoclinal ridges rising 2000 to 3000 ft.
Associated with these irregular escarpments are occasional rectilinear ridges, the work of extensive erosion on monoclinal structures, of whick Echo Cliffs, east of the Painted Desert (so called from its manycoloured sandstones and clays), is a good example.
In the north, where dislocations have invaded the field of the horizontal Columbian lavas, as in south-eastern Oregon and north-eastern California, the blocks are monoclinal in structure as well as in attitude; here the amount of dissection is relatively moderate, for some of the fault faces are described as ravined but not yet deeply dissected; hence these dislocations appear to be of recent date.
The older rocks are like those of Bengal, and the newer beds show no sign of either the Himalayan or the Burmese folding - on the top of the plateau they are nearly horizontal, but along the southern margin they are bent sharply downwards in a simple monoclinal fold.