134 
UTAH PENEPLAINS 
sandstone rests directly upon the pre-Cambrian crystallines just 
as it does on the summit of the uplift, on Triassic beds, and on 
Jurassic strata. This relationship is well displayed in the Black 
Canyon of the Gunnison River, and on Grand River west of 
Grand Junction. 
Beyond the Green River the Dakotan sandstone is well displayed 
in the San Rafael Swell and in the Wasatch Plateau east of the 
Wasatch Mountains. Dutton also records it at many localities 
farther south. More or less deeply buried over much of the High 
Plateaux region the Dakotan sandstone nevertheless reaches sky 
at many points; so that the uneven basal plane is an easily 
reognizable guide-horizon, and its local position is always readily 
estimated. From its basal horizon to the next higher great plane 
of unconformity the vertical distance is often not less than 5000 
feet. 
Everywhere on the west side of the Cordillera where the Dakota 
sandstone is fully exposed it is found that the surface upon which 
it rests is an erosion surface just as it is on the east flank of the 
Rockies. From the High Plateaux area the old planation sur¬ 
face as it approaches the Rocky Mountain uplift rises out of the 
lower levels, mounts the flanks of the great arch, and finally 
seems to merge with the Summital Plain over the crest. It is 
also traceable around the southern end of the Rockies and con¬ 
nects with the similar plain on the east flank in northeastern New 
Mexico. Thus followed both over the crest and around the base 
of the uplift this erosion-level appears to correspond with the 
Corazon peneplain. There seems to be but little doubt that this 
is the correct correlation. 
A Laramian hiatus in eastern Utah is a new conception. Few 
geological formations were so long so widely misunderstood as 
the Laramie beds of the Rocky Mountain region. As typically 
developed in Wyoming they comprised a great succession of 
shales and soft sandstones in which were often so many beds of 
lignite interspersed that the section was also denominated the 
Lignitic Group and regarded as Tertic in age. 
The coal-bearing feature was highly misleading; and many a 
determination made on this one characteristic alone proved most 
disastrous to correct correlation. Singularly, the great succes- 
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