6 BULLETIN 1001, TJ. S. DEPARTMENT OF AGRICULTURE. 
The " humid region" [8] 7 is that area in which some sort of crop 
may be produced on cultivated land every year. 'Except for small 
areas in the higher mountains to the south or on the higher plateaus 
or valleys to the north this humid region occurs east of the ninety- 
seventh meridian or west of the Cascade Mountains. Irrigated lands 
would fall in this class; although they are not in a humid region, the 
growing conditions supplied the plants are those of a humid region. 
" Forests" and " woodlands" [8] are, as the terms imply, the tree- 
bearing areas. In the region under consideration they lie, for the 
most part, within the national forests. In so far as they have grazing 
uses they are now very properly treated as arid grazing land, with 
scattered small areas of dry-farming land interspersed. However, 
they are not considered as belonging in the area here referred to as 
arid grazing land which lies outside the national forests. 
Of course, these subdivisions are more or less arbitrary, but they 
are necessary in order that we may consider the best utilization of 
the different regions with some degree of accuracy. 
There is a belt or zone between the farming land of the humid 
region and that of the semiarid region that may be handled as humid 
farming land only part of the time, and an adjustment in the cropping 
systems is necessary to meet this condition. Likewise there is a belt 
between the dry-farming land and the arid grazing land, in which 
part of the land may be dry farmed with success only part of the 
time. And there is a strip around the desert area that may be 
grazed for a longer or shorter time at irregular intervals, but not 
throughout the year at any time, and frequently not at all during a 
given year. 
These areas of variable productivity cause much trouble when an 
attempt is made to show upon the map the boundaries of each kind 
of land, because the boundary is a zone and not a line. These tran- 
sition areas will not continuously produce when operated under the 
more complex; type of organization to which they are occasionally 
adapted; hence they must be operated all the time under a lower, 
but safe type, and the system of management. made flexible enough 
to accommodate itself to the periods of more than the assured 
production. 
The determining natural conditions are not the average climatic 
conditions. They are the absolute minima, and the relative fre- 
quency with which these minima may be expected to occur. We do 
not need to be told that citrus fruits can not be grown with profit in 
a region where the temperature goes to zero for a longer or shorter 
time one year in five, no matter what it may do the other four years; 
but it seems to be necessary to demonstrate by trial and failure that 
» The bracketed figures used throughout this bulletin refer to the publications listed in the bibliography 
on pages 68 et seq. 
