Geology of Ft. Apache Region, Ariz. — Reagan. 281 
Seven-Mile hill section and in the Salt river and Hinton re- 
gions, accumulated through the Tertiary and may have begun 
even earlier. The Tertiary rocks begin with a consolidated, 
coarse, conglomerate series, beneath which are strata of partly 
lithified to lithified sands, clays and gravels reaching a thickness 
of nearly a thousand feet in most places. The formation is found, 
for the most part, in the ancient canyons of the region and in- 
dicates a laking stage, caused by the seismic disturbances dur- 
ing the Tertiary. These will be further considered under the 
next subject. 
The Quaternary. — Conformably superimposed on the Ter- 
tiary are hundreds of feet of unconsolidated gravels and clays 
and occasionally volcanic ashes. This series covered the entire 
region, except possibly the Ellison dome, so that the. lava flows 
which closed the epoch flowed over a plain. Since then much 
of it has been removed so that now it is patchy except where 
protected with superimposed lava. It now fills all the vallevs 
in the Pinal and Apache mountain districts: the volcanic and 
plutonic rocks projecting above it as peaks and mountain 
ridges. The middle Cherry Creek valley and the Tonto basin, 
as well as the Ellison flat, are covered with it. It covers the 
Mogollon mesa together with its southern prolongations to a 
thickness of from 500 to 1000 feet. It is the surface rock of 
the Kelley butte country, and extends beneath the lava of the 
Nantan plateau as far as visited. 
Cause of the Deposition of the Quaternary and Tertiary 
deposits. — It was found on observation that the gravels and 
cobble-stones of the Tertiary and Quaternary formations were: 
schists, quartzytes, gneisses. Carboniferous rocks, vitreous Ton- 
to sandstone, diorytes, trachytes and Archrean rocks. The first 
opinion of the writer was that the formation was of glacial 
origin; but careful examination showed no stride markings. 
Moreover, many of the rocks were found to be angular and not 
much if at all water worn. So the glacial origin theory had to 
]).' abandoned. 
The next feasible theory that suggested itself was that of 
depression, but since the Salt river, Hinton, and Globe de- 
posits are 4000 feet below those on the Mogollon range yet no 
indication of a brackish or salt sea is to be found in them, it 
was necessary to abandon the depression theory also. 
