SOUTHERN PACIFIC LINES 203 
Just east of the bridge over the Salt River is Tempe Butte (see 
fig. 50), a prominent landmark due to a heavy mass of lava (andesite) 
lying on shale and sandstone, which with the lava is tilted to the 
southeast at an angle of 45° or more. The base is a massive sand- 
stone quarried to some extent for building. The strata are more and 
more mixed with clay toward the top, where most of the material 
under the lava is red shale. More red sandstone in massive beds is 
exposed north of the river opposite Tempe; it grades down into a 
coarse granitic arkose or breccia lying on an irregular surface of old 
granite. It dips 65° NW., nearly at right angles to the dip of the 
exposure in Tempe Butte. This sandstone was found in a well 1% 
miles northeast of Tempe, but a well 2% miles northwest of the town 
was entirely in granite. Similar arkose and conglomerate lie on 
granite in Camelback Mountain, near Phoenix. Probably the age of 
the formation is late Tertiary. (Lee.) Other buttes, including Bell 
Butte,* rise out of the valley a short distance southwest of Tempe. 
N. oe Butte s. 
Horizontal stalk 
re) 1,000 Feet 
j 
| are i i. 
‘Vertical scale 
000 Feet 
ee i i 
Figure 50.—Section through Tempe Butte and Tempe Well, Ariz. After Lee 
Just north of the river north of Tempe sedimentary rocks of Ter- 
tiary age form a small group of picturesque hills included in the 
Saiuaro National Monument. Here the material is an arkosic con- 
glomerate in massive beds lying in part on granite gneiss and in part 
on a porphyritic felsite. The conglomerate contains much granite 
and some schist and felsite with many fragments from 6 inches to 
6 feet in diameter. In places there is but little matrix, but in general 
the coarse material is embedded in sand composed of grains of quartz 
and feldspar. It has been suggested that these rocks are of Triassic 
age, but here, as in Tempe Butte, they include a thin basalt flow and 
are capped by basalt, a succession closely resembling that which is 
found in the Tertiary of the surrounding region. The tilting of the 
Tertiary beds here and elsewhere in the Phoenix region shows that 
there have been earth movements in this region in post-Tertiary time, 
and the similar tilting and faulting of the volcanic succession in 
46 The rock of Bell Butte under the | of hernttende and feldspar of the soda- 
microscope proves to be a hornblende- | lime group. The is glassy, 
pyroxene andesite showing phenocrysts | in part microlithic. (Lee.) 
