6 
Coi^ORADo Experiment Station 
Quite a large number of soil types occur, many of which have 
a considerable distribution. The soils deposited as the result of 
the work of the Rio Grande commence at Del Norte and extend 
eastward to Mo-sca, Hooper and Alamosa, and westward to the 
mountains. Most of these soils are rather porous and gravelly, 
underlaid by gravelly subsoils. In color they are mostly reddish 
brown. These soils have been called by the Bureau of Soils the 
San Luis Series.* In this region are found sands, sandy loams 
and loams, which the Bureau of Soils has called San Luis Sand, 
San Luis Sandy Loam, and San Luis Loam, respectively. 
The San Luis Sand extends from the face of the mountains to 
the vicinity of Center and Monte Vista and eastward from those 
towns in narrow belts as far as the Valley trough. The type is por¬ 
ous and easily worked, being derived from the volcanic rocks on the 
adjacent mountains. The lighter portions are subject to wind 
drifting, and frequently form slight ridges or dunes. The subsoil 
is gravelly and occurs at depths of twO' to^ four feet. This soil 
never becomes sticky when wet, water penetrates it readily and 
drainage is rapid where the slopes and other conditions permit. 
Some of the lower slopes, due to insufficient natural drainage con¬ 
ditions, are swampy and alkalized. New lands of this type fre¬ 
quently have a cemented area or layer which occurs at about the 
depth of the rainfall’s penetration. The cemented area has'been 
caused by the washing down of soluble materials from the surface 
and their deposition in a layer at the bottom of the zone of per¬ 
colation. Irrigation has dissolved these cementing materials and 
on old irrigated lands this layer, sometimes called hardpan, is not 
noticeable. 
In this area the next most extensive type of soil is the San 
Luis Sandy Loam. This contains more fine material than the San 
Luis Sand previously described but is, on the whole, rather coarse 
and carries considerable gravel. The surface layer is from i8 to 
36 inches in depth underlaid by coarse gravelly subsoil. It is quite 
sticky when wet, especially as there are often streaks of heavier 
material in the surface. Except in the lower lying districts this 
type is naturally well drained. 
The San Luis Loam' occurs in limited patches on the lower 
rivers and usually upon the low slopes adjoining such areas. The 
soil is rather heavy and contains a great deal of the finer material 
carried down by mountain torrents, or washed from higher lying 
soils. It looks much like San Luis Sandy Loam, but contains a 
* Soil Surveys of the San Luis Valley, Colorado Field Operations, 
Bureau of Soils, 1903. Circular No. 52, Bureau of Soils, 1912. 
