38 GUIDEBOOK OF THE WESTERN UNITED STATES. 
on the south side. For many miles the surface is made up of sand 
and loose sandstone or conglomerate of Tertiary age. The valley 
has been cut by the river to a depth of 250 feet below the adjoining 
great plateau, but it is partly filled with about 100 feet of sand and 
clay (alluvium) deposited by the stream, and these materials are 
still in course of deposition. In places the valley is cut through the 
Tertiary deposits into underlying shale and limestone of Upper 
Cretaceous age, but these do not appear at the surface until they rise 
in the valley slopes near Hartland. In ascending the valley the 
railway skirts slopes that rise 100 feet or more above the river flat 
to a plain of remarkable smoothness which ascends gradually west- 
ward at about the same rate as the upgrade of the valley. In these 
slopes are widely scattered outcrops of the Tertiary deposits—loam 
and sand with interbedded hard layers of coarse sandstone or con- 
glomerate of gray color or of white ‘grit’? consisting of sand and 
gravel cemented with calcium carbonate. 
At a point halfway between mileposts 358 and 359, 6 miles west of 
Dodge, a small exposure of conglomerate is visible from the train. A 
granite marker at this place indicates the former course of the Santa 
Fe Trail, which extended up the north or American bank of the river 
very near the course of the present railway line from Dodge to 
Bents Fort, Colo. 
Several small ledges of conglomerate appear for a short distance 
on the north side of the track at Howell and again just beyond 
milepost 363, a mile and a half west of Howell. At 
ree milepost 365 the sand hills on the south side of the 
Kann theat mites, Valley are visible, and they extend almost continu- 
ously along that side of the river into Colorado. 
In places high on the slopes to the north may be seen an irrigation 
canal intended to carry water from the river to the high plain north of 
Dodge and thence to Wright and Spearville. The intake of this canal 
is a short distance west of Ingalls, and by following a grade somewhat 
less than that of the fall of the river, the canal finally reaches the level of 
the plains at a point 3 miles northwest of Dodge. The Arkansas is a 
stream of large annual flow, but as much of its water is carried at times 
of freshet and as the volume at other times is exceedingly variable, 
there is often considerable difficulty in maintaining a regular supply 
in the canal during the growing season. In the future, no doubt, 
the freshet waters of this river, as well as of most other large streams 
in the United States, will not be allowed to escape but will be held 
in suitable storage reservoirs to maintain a flow. 
It will be noted that west of Dodge the valley contains fewer trees 
than it does to the east and that still farther west in the region of 
more arid climate the trees along the valley diminish greatly in num- 
ber. There are also fewer cultivated fields, although some alfalfa 
