124 LINE FROM BASE OF THE MOUNTAINS TO PUGET SOUND. 
terminating a grand plateau of five or ten miles in width, gently sloping to the north, and 
reaching to a wooded ridge, running nearly parallel with the river. Numerous small streams rise 
in this ridge, and, cutting the plateau into deep ravines, are eventually discharged into the Colum- 
bia. Passing down the Columbia from Wallah-Wallah to the Dalles on the north side of the 
river, the party of Mr. Tinkham found it necessary in only two instances to cross the rocky spurs 
jutting out from the river bluffs. 'The grades for the balance of the route to the sound will be 
very easy, and the work light; the heavy work being the rock-cutting where the bluffs encroach 
upon the river, the extra provision needed to preserve the embankments from the wash of 
freshets, and the possible necessity of a short tunnel at Cape Horn. The bluffy country border- 
ing on the Columbia ceases near Cape Horn. From below the Dalles the woods commence, and 
so continue to the head of Cowlitz river. The wide and comparatively flat and wooded valley 
of the Cowlitz connects with plains, sometimes of prairie, and sometimes of woodland, extending 
to Puget sound, which, although not fully explored, are sufficiently well known to insure 
the unusually favorable character of the country for the construction of a railway. 
The earth excavation and embankment will not probably exceed the heaviest work of the 
prairies east of the mountains, and is estimated not to exceed an average of seven to eight feet. 
The material for the embankment is almost always of a superior character. The Great Plain 
of the Columbia, and the valley of the Columbia, afford a great deal of loose, pebbly matter 
trom the disintegrated fragments of the trap rock, which will frequently be found to be of much 
value. Sand in portions of the valley of the Columbia covers extensive plains, and fine gravel 
plains characterize the Cowlitz valley and the intervale to the sound. 
The amount of rock-cutting, with the exception of the portion of the line between the Dalles 
and Cape Horn, will be very small. A portion of the excavation on the first part of the Spo- 
kane Plain will be rock ; occasional rock-cuttings will be required in the Columbia River valley, 
and a small tunnel of seven hundred feet in length may be required at Cape Horn. The rock 
in this region is generally a basaltic trap. 
No grade higher than forty feet will be necessary in this section, and for nearly the whole dis- 
tance the gradients will be very gentle. The average declivity of the valley of the Columbia is 
inconsiderable, being less than two feet per mile. Cowlitz river has a small descent per mile. 
As a whole, the culvert work will be very small in amount, falling chiefly upon that portion 
embracing the tributaries of the Cowlitz, and the small streams making down from the western 
slopes of the Cascades. The great item in bridging is the crossing of the Columbia river, 
near Wallah-Wallah. But little data is obtained for this crossing ; but if the river be bridged 
near the mouth of Snake river, as indicated on the map, the approaches are here favorable, and 
the length of the bridge will be about four hundred and fifty yards. Further careful examina- 
tion is required to determine the best position for the crossing. 
The route for nearly one-half of this section is through woodlands; the balance is destitute 
of wood on the immediate line of the road. The Great Plain of the Columbia, and the Colum- 
bia river bottoms as far down as the Dalles, lack wood. Thence forward to Puget sound the 
route is through heavy forests, principally of the fir and cedar, and abounding with valuable 
lumber. There will be little difficulty in furnishing the line with all lumber required in its con- 
struction. The interval in the Spokane Plain, wholly destitute of trees, is about 110 miles in 
extent; rests on extensive districts of pine, cedar, larch, &c., at its eastern edge; and on the 
west, touches on the water of the Columbia, reaching north into a wooded country, and offering 
easy opportunity for rafting logs and lumber from above. 
The wooded ridge beginning at about thirty miles distance from the mouth of Snake river, and 
running nearly parallel with the Columbia at five or ten miles distance from it, is densely covered 
with a large growth of timber, probably corresponding with the mixed growth of pines, firs, 
&c., on the eastern base of the Cascade mountains, with which it finally connects. From the 
ease with which this growth can be reached from the Columbia, and the facilities aflorded by 
