CHAPTER XI. 

 SEVIER AND PAUNSAGUNT PLATEAUS. 



General structure and form of the Sevier Plateau. — Sculpture. — Ravines. — Superposed features and 

 details. — Northern portion of the plateau. — A gigantic cliff.— Monroe Amphitheater. — Lava heds 

 exposed within it. — The Gate of Monroe. — Propylitic masses. — Clastic volcanic heds at the base 

 of the series. — Hornblendic andesites. — Intervening period of erosion of the propylites. — Horn- 

 hlendic trachytes and augitic andesites. — Argilloid and granitoid trachytes. — General succession 

 of the eruptions. — Comparison with the succession found in the Auvergne. — Eastern side of the 

 Sevier Plateau and Blue Mountain. — Great extent of the emanations from the principal volcanic 

 centers of the northern part of the plateau. — Eroded lava-capped mesas around Salina Canon. — 

 The Black Cap. — Augitic trachytes. — Lava sheets south of Monroe Amphitheater. — Central vents 

 of the Sevier Plateau. — Volcanic conglomerates. — An ancient cone, buried in lava and exhumed 

 by erosion. — Conglomerates south of the central vents. — Southern focus of eruptions. — Andesitic 

 conglomerates. — Southern termination of the Sevier Plateau. — General succession of eruptive 

 sheets. — Sections. — East Fork Canon. — Effect of the Sevier fault. — Tufacpous deposits exposed in 

 East Fork Canon. — Their transitional characters. — Their metamorphism and the resemblance of 

 the metamorphs to lava sheets. — Phonolite hill. — Grass Valley, its structure and origin. — Exist- 

 ence of an ancient lake in Grass Valley. — The causes which produced it. — Tufaceous deposits of 

 Mesa Creek. — Their recent formation.— Their transitional characters. — Alluvial cones of Grass 

 Valley. — The Paunsagunt. — Lower Eocene beds. — Faults. — The southern terraces. — Paria Valley. 

 — A grand erosion. — The scenery of Paria Valley. — Table Cliff and Kaiparowits Peak. — The Pink 

 Cliffs and architectural forms sculptured from them. — A recent basaltic cone. — Scattered basaltic 

 craters of the southern terraces. 



The Sevier Plateau is next to be described. It is a long and rather 

 narrow uplift, having a fault along its western base and inclining to the 

 eastward; at first very gently, then with a stronger slope, which grades 

 rapidly down into Grass Valley. The length of this table is about 70 

 miles, and its width varies from 10 to 20 miles. It is, therefore, long 

 and narrow like the general ground-plan of a mountain range. But its 

 structure has very little analogy to ordinary mountain uplifts. It has no 

 sharply upturned strata upon its flanks reclining against a core of rneta- 

 morphic rocks — no summit ridge marking- the axis along which granitoid 

 and schistose rocks have been protruded, nor even the monoclinal ridge 

 which characterizes the Wasatch and Basin Ranges. It is a tabular mass 

 very like the inclined blocks of the Kaibab region to the southward. The 

 inclination is very small, seldom exceeding three or four degrees upon the 



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