114 LANDS OF THE ARID REGION OF THE UNITED STATES. 
of the land can be utilized. But there is also a limit to the amount of 
water that can be profitably employed on a unit of land, and where the 
supply of water is in excess of the quantity required by such lands as are 
properly disposed to receive and use it, only a portion of the water can be 
utilized. In order to ascertain, therefore, the extent of agricultural land in 
a given district, it is necessary to make a measurement of land, or a 
measurement of water, or perhaps both, and it is necessary to know the 
amount of water demanded by a unit area of the land under consideration. 
The proper quota of water for irrigation depends on climate and soil 
and subsoil, as well as on the nature of the crop, and varies indefinitely 
under diverse conditions. Asa rule, the best soils require least water; those 
which demand most are light sands on one hand and adhesive clays on the 
other. Where the subsoil is open and dry, nore water is needed than where 
it is moist or impervious. Wherever there is an impervious substratum, the 
subsoil accumulates moisture and the demand for water diminishes from 
year to year. ‘These and other considerations so complicate the subject 
that it is difficult to generalize, and I have found it more practicable to use 
in my investigations certain limiting quantities than to attempt in every 
case a diagnosis of the local conditions. By comparing the volumes of 
certain streams in Utah, that are now used in irrigation to their full capacity, 
with the quantities of land that they serve, I have found that one hundred 
acres of dry bench land (7. ¢., land with a deep, dry, open subsoil) will not 
yield a full crop of grain with less than one cubic foot of water per second, 
and this under the most favorable climate of the Territory. Where the 
climate is drier, a greater quantity is required. Where there is a moist 
subsoil, a less may suffice. 
In the drier districts, where the streams are small, they are usually 
employed upon the dry benches, because these are most convenient to their 
sources; and it is very rarely the case that their utility is increased by the 
presence of a moist subsoil. But it is also in the drier districts that the 
extent of agricultural land is ascertained by the measurement of streams ; 
and hence there is little danger of error if we use in all cases the criterion 
that applies to dry bench land In the discussion of the lands of northern 
Utah, I have therefore assigned to each cubie foot per second of perennial 
