Geology of Ft. Apache Region, Ariz. — Reagan. 269 
yond the Apache and Pinal mountains to the region of the "lost 
mountains" of the lower Gila valley. On each side everything 
is bathed in the most delicate tints and everything lies deathlike 
in the peculiar intangible afternoon haze of the region which 
seems to magnify distant details rather than subdue them. The 
wonderful monotony seems uninclosable in any horizon and one 
imagines the scene to continue on always the same and with- 
out end. 
STRUCTURE. 
The rocks of the region are intrusive, extrusive, and sedi- 
mentary. 
The intrusive rocks are the laccoliths, dikes, volcanic necks 
and intrusive sheets of the region ; the extrusive rocks are the 
lavas and tuffs that overspread the greater part of the country; 
and the sedimentary rocks, the deposits that were laid down in 
the seas and lakes in almost continuous series from the earliest 
known geologic time to the most recent. 
The Sedimentary Rocks. — Among the level canyon-cut 
rocks of the plateau part of the region, the sequence of strata 
is never lost. Save where covering lavas are crossed, there is 
no break in the observation. One bed is followed with the eye 
until it either dips beneath the surface or is ended by denud- 
ation and another bearing a definite relation to it is taken up. 
An unconformity is usually seen at a glance. But in the 
Apache and Pinal mountain area southwest of the Plateau the 
case is reversed. The mountains divide the space with the val- 
ley gravels and the eruptive rocks serve to mask the sediment- 
ary deposits. The outcrops of the latter are reduced to the con- 
dition of peninsulas or islands each of which is a problem in 
itself. 
The dip of all the sedimentary deposits east of the longitude 
of Canyon creek is north and east. West of that line and north 
of Salt river the dip is north or north and west, while south of 
that river the dip swings around from southwest via the south 
and southeast to a northeast dip. 
The geologic systems represented are the following: 1, 
Quaternary ; 2, Tertiary ; 3, Cretaceous ; 4, Aubery Group ; 5, 
Upper Red Wall Group ; 6, Lower Red Wall Group ; 7, Devon- 
ian ; 8, Upper Silurian; 9, Tonto Group; 10, Algcnkian ; Vol- 
