TITE SANTA FE ROUTE, 
115 
At Angell and for several miles west many cinder cones are visible 
on the widespread lava sheet which begins a short distance north of 
that siding. Most of these cones are from 150 to 250 
F ON fant 
Kansas City 1,243 miles. 
in 
feet high. They consist of piles of loose, dark vol- 
canic cinder or pumice which varies from pieces 2 
ches in diameter to fine sand. The deposit in- 
cludes volcanic bombs, rounded masses of more compact lava, which 
were ejected from Peloatid vents. 
This region of lava occupies an 
area about 15 miles wide from north to south and 70 miles long from 
east to west, with the San Francisco Mountains near the center. It 
has been designated the San Franciscan volcanic field.1 
‘Three general periods of volcanic ac- 
tivity are indicated in this field. First 
from numerous cracks in 
the limestone and underlying strata in 
a very fluid condition and spread widely 
over the gently sloping surface of the 
Mountain, Kendrick Peak, Elden Moun- 
tain, O’ Leary Peak, and other high 
summits. e lavas, being less fluid 
than the ie. basalt, piled up and in 
part arched up on it in high mounds of 
relatively small extent. As these rocks 
d massive they give rise to 
very prominent topugraphic features. It 
is “dS cried that there was a considerable 
tval of time between the first basalt 
pic oa and the outflows of less fluid 
lavas, but apparently all of them were 
extruded late in Tertiary time. There 
are also bodies of intruded rhyolite which 
apparently cut across the earlier basalt 
at several localities, notably in Sitgreaves 
Peak, Government Mountain, an 
O’Leary Peak. This rhyolite is a light- 
gray or nearly whe rock, usually break- 
ing into thin sla 
In the third nan of eruption in the 
Francisco volcanic field occurred an 
extensive outflow of black lava (basalt) 
similar to the first. It came out of nu- 
cracks and other orifices, mostly 
within the area of the earlier lava sheets. 
The lava at many localities ran down 
valleys which had been eroded in the 
| & cone, as a rule 
earlier lava sheets or the underlying lime- 
stone in the interval between the periods 
of eruption. Most of this cat lava is 
exceedingly fresh in appeara: 
to that occupying the San Jose RES ee at 
Grant and McCartys, N. Mex., which is 
described on pages 97-98. 
At many of the vents the cessation of 
lava flow was followed by an outburst of 
cinders and ash. This material was 
thrown up into the air for some distance 
and, settling back about the vent, formed 
with a central crater. 
The building of these cinder cones usually 
marked the last stage of activity of the 
of the cone. The lava 
volume of steam, for sates ot} it is petie 
porous, owing to the expansion of the 
steam in the cooling rock as it flowed out 
over the surface. The cinder consists of 
lava filled with small steam holes, so 
that most of it is completely porous or 
In the- cinder cones are 
usually included masses of compact lava 
probably thrown out as bombs. 
Sev- 
eral of the cinder cones doubtless date 
back to the earlier basalt eruption, but 
most of them appear to belong to the last 
period. 
