166 
GUIDEBOOK OF THE WESTERN UNITED STATES, 
Near milepost 192 a branch line of the road enters the valley from 
the right and gradually descends along the valley wall. This branch 
unites with the main line at Connell and serves to 
Connell. 
Elevation 845 — 
Population 778. 
St. Paul 1,615 een 
connect this place with Coulee City and the Big Bend 
country to the north. 
Below Connell the valley walls grow more rugged, 
and at Cactus siding (milepost 200) a very prominent 
wall of lava is seen on both sides of the valley, but more particularly 
deposition of these beds was interrupted 
by a flow of basaltic lava which was the 
beginning of a great series of flows that 
reached their maximum development in 
the succeeding Miocene epoch. 
Sheet after sheet of basaltic lava was 
ed out over a territory 250,000 square 
miles in atte that included the greater 
part of Washington, all of eastern Oregon, 
part of Miprse- 5 and a large area in the 
Snake River valley of Idaho. (See map 
of Columbia River plateau on sheet 23.) 
It is probable, however, that the erup- 
tions in the Washington area began at a 
somewhat earlier date than those of the 
Snake River plains of Idaho, which seem 
to have been in part contemporaneous 
with the last flows that occurred along 
Columbia River. 
It is a generally accepted view that 
mely 
mainly on the following evidence: ie 
The volume and extent of _the la 
nary craters; (2) the rarity of the frag- 
mental materials 
acteristic of crater eruptions; (3) old fis- 
sures res through which the floods - t lava 
now ea with the cooled pas Renee 
es oa, SaaS 1. Lt me me 
lying sheets of lava. 
The basalt was not poured forth in one 
great outburst, but is made up of a great 
_ Bumber of layers or individual flows 
which in places are of feet in 
aggregate thickness. _About 20 such flows 
bia River. Each one represents a dis- 
for they are marked by beds of soil in 
which trees grew to considerable size 
before being charred and buried by later 
ows. The eruptions of lava, especially 
in the later stages of activity, were sepa- 
rated also by periods in which other 
materials accumulated, consisting of vol- 
canic ash and beds of sand, clay, and 
gravel laid down in Jakes or rivers. 
In addition to the massive flows that 
constitute the greater part of the forma- 
try, or, mixed with hot 
water, have flowed over the surface as 
aud The fragmental materials are not 
sy widely 
The quantity of cael eS out 
during this iod was en The 
greatest thickness of the ee aa asso- 
ciated deposits is not less than 4,000 feet, 
but if it averages only 500 feet thick over 
the avery moderate 
estimate, it would “make a mass of 24,000 
cubic miles, or a cube nearly 30 miles in 
| height. Even this great volume may be 
far less than that actually poured out. 
Coincident with the later stages of the 
lava eruptions occurred a subsidence of 
the ara * at at ae 1,2 
and a large lake was ‘formed, in whee ie 
area on the west. Before the basaltic 
eruptions had ceased a great volcanic dis- 
turbance occurred in the Cascade region 
and lava of another kind (andesite) was 
