TERREPLEINS OF UTAH’S PLATEAUX 
55 
north flank of the latter they recline as remnantal patches of 
great sections of soft deposits which elsewhere have been com- 
pletely stripped off the indurated Paleozoics that constitute the 
foundation of the broad arch. The High Plateaux appear to 
owe their belated preservation to Tertiary extravasation of lavas 
that serve as protecting caps for the unconsolidated strata be- 
neath. Were it not for these remnantal tablelands long and ex- 
citing chapters in the history of the Cordilleran region would be 
lost beyond possible rescue. 
Like so many of the neighboring Great Basin ranges the High 
Plateaux stand 11,000 to 12,000 feet above sea-level, and 5,000 
to 6,000 feet above the valley floors between — the present gen- 
eral plains surface. Comprising as they do, a dozen or more 
lofty eminences, they have flat- topped summits of such limited 
extent that they now are really narrow mountain ridges not es- 
sentially distinct from the other desert ranges. They differ from 
the ranges of the Great Basin lying to the west only in the cir- 
cumstance that the remnantal lava sheets which surmount them 
still preserve traces of the original high plains surface, whereas the 
mountain blocks not so protected, comprising the other desert 
ranges, do not. 
Because of the light which they recently shed upon the physio- 
graphic development of the arid part of our continent the High 
Plateaux of Utah possess unusual interest. Strangely they give 
a clue to the origin of the bare desert ranges to the west of them, 
and to the forest clad chains to the east. Arid Great Basin Range 
and pluvial Cordillera thus really evolve along parallel lines. The 
Utah heights not only connect the mountains of two climatic con- 
