114 GUIDEBOOK OF THE WESTERN UNITED STATES. 
and culminate in the high peaks of the San Francisco Mountains, 25 
miles away, which are prominently in view for many miles along the 
railway. 
_ At milepost 320 there is a cinder cone a short distance north of the 
railway, with a lava flow extending from its base to the east and 
another to the south, the latter reaching nearly to the track. The 
cone is remarkably symmetrical and fresh looking, and the lava flow 
is closely similar to that which is exposed near Grant and Horace, 
220 miles farther east. A short distance north of the cone is the south- 
ern margin of a wide area of lava (basalt), which extends far to the 
north as well as to the northeast and northwest. On its rugged sur- 
face are many cinder cones which are visible more or less distinctly 
from the train. (See Pl. XXVII.) 
Between mileposts 319 and 320 is a signboard reading ‘“ Eastern 
boundary Coconino National Forest.” This forest is one of two 
Government reservations which include the great forest of yellow 
pine (Pinus ponderosa) covering the higher part of the Arizona or 
Coconino Plateau.* ; 
As the limestone plateau is ascended, the first trees observed are 
stunted junipers and pifions; these rapidly increase in size and abun- 
dance as the higher altitudes are attained, a feature especially notice- 
able between Angell and Winona sidings. 
' These great forests extend northwest- 
ward to the Grand ard 
to the southern margin of the plateau. 
They include about 1,317,000 acres of 
western yellow pine. In parts of the 
forest and in a broad zone around its mar- 
turn is largely controlled by the altitude. 
Accordingly the pine growth is nearly all 
in the area higher than 6,200 feet, for at 
is insufficient; in fact, even in some of the 
western portions of the high plateau, 
here the altitude is slightly above this 
amount, the rainfall is 8 
tude of 12,000 feet on the San Francisco 
Mountains. 
The investigations of the Geological 
Survey and the Forest Service on the 
relation of forests to water supply and soil 
districts conserve the precipitation for 
stream flow and increase the underground 
storage of water. The trees break the 
violence of the rain, retard snow melting, 
and increase absorption by the soil, all of 
which diminish erosion of the surface and 
rapidity and volume of run-off, Under- 
ground seepage is increased, so that a 
steady flow is maintained in springs 
and , and less silt is removed, 
hence there is less to obstruct the stream 
beds. 
Fires have ravaged many parts of the 
forests, and one of the principal functions 
of the Forest Service is to prevent or ex- 
were struck in three years in the high 
nlat : f Arizona | adioini 
5 
regions. : 
Ts elaciaaalitens Spice Sebi oe 
