76 LANDS OF THE ARID REGION OF THE UNITED STATES. 
supply is therefore represented by a sheet 1.9 inches in depth covering 
the entire district. 
The indirect influence of ‘irrigation, and the influences exerted by the 
grazier and the woodman, cannot be estimated from any existing data, but 
of their tendencies there can be no question. To some extent they diminish 
local evaporation, and induce a larger share of the rainfall to gather in the 
streams; and to one who has contrasted the district in question with 
similar districts in their virgin condition, there seems no extravagance in 
ascribing to them the whole of the observed change. 
In the valley of the Mississippi and on the Atlantic coast, it has been 
observed that the floods of rivers are higher than formerly, and that the low 
stages are lower, and the change has been ascribed by Ellet and others to 
the .destruction of the native vegetation. The removal -of forests and of 
prairie grasses is believed to facilitate the rapid discharge from the land of 
the water from rain and melted snow, and to diminish the amount stored 
in the soil to maintain springs. In an arid country like Utah, where 
the thirst of the air is not satisfied by the entire rainfall, any influence 
that will increase the rapidity of the discharge must also increase the 
amount of the discharge. The moisture that lingers on the surface is 
lost. 
On the whole, it may be most wise to hold the question an open one 
whether the water supply of the lake has been increased by a climatic 
change or by human agency. So far as we now know, neither theory is 
inconsistent with the facts, and it is possible that the truth includes both. 
The former appeals to a cause that may perhaps be adequate, but is not 
independently known to exist. The latter appeals to causes known to 
exist but quantitatively undetermined. 2 
It is gratifying to tun to the economic bearings of the question, for 
the theories best sustained by facts are those most flattering to the agricul- 
tural future of the Arid Region. If the filling of the streams and the rise 
of the lake were due to a transient extreme of climate, that extreme would 
be followed by a return to a mean condition, or perhaps by an oscillation 
in the opposite direction, and a large share of the fields now productive 
would be stricken by drought and returned to the desert. 
