FRAMEWORK OF ARIZONA 
249 
Archuleta ^ formation of the San Juan region. This, with some 
other associated beds, constitutes the Aztecan series. Above it 
come in the Puerco clays of New Mexico, named by Cope in 1875, 
but which Gregory, forty years afterwards, proposes to give the 
new title of Tohachi shale. Newberry’s Canyon Largo sand¬ 
stone of New Mexico appears to be the thick sandstone capping 
the Chuska range, to which Gregory applies an entirely new desig¬ 
nation, the Chuska sandstone, without reference to Newberry’s 
work of half a century before. 
Mid Tertic, or Miocene, deposits seem not to be in evidence in 
northeastern Arizona; but in the northwestern corner of the state 
they appear in strong development in the Grand Wash and in the 
Virgen River valley, just over the line in Nevada. In the San 
Pedro River valley, in the southern part of the state, round about 
Benson, extensive clays probably represent Miocene and Pliocene 
depositions. They are fossiliferous. 
Both the Late Tertic and Quaternaric deposits are, on the whole, 
too distantly related and too far removed from one another to 
permit of satisfactory classification at this time. 
The remarkable conglomerates of the Gila Basin, named so ear¬ 
ly as 1875 by Gilbert, who described them as wide-spread valley 
deposits, sometimes attain a thickness of 1,500 feet. Consolidated 
gravels of this sort extend far eastward into New Mexico; and 
occupy many river valleys throughout the Southwest. 
It may be, that when the orogenic movements of late geological 
times in the region are closely evaluated, these isolated deposits 
will be adjusted stratigraphically to one another. Such deposits 
represent in many cases ephemeral empondment of stream waters 
through damming by lava flows. Correlation of temporary epiro- 
tic deposits is not accomplished readily because it involves the 
consideration of erosion laws entirely distinct from those which 
we are accustomed to in pluvial lands; and adequate methods of 
work are not yet formulated. 
Tabulation of the geological formations of the state so far as 
now understood is annexed: 
2 Shaler’s name Animas for these beds in southwestern Colorado is preoccupied; 
see Proc. Iowa Acad. Sci., Vol. XXII, p. 260, 1915. 
I 
