The area covered is all 11 far western contiguous States, 
Washington, Idaho, Montana, Oregon, California, Nevada, 
Utah, Wyoming, Colorado, Arizona, and New Mexico, also 
Trans-Pecos Texas. Coverage extends eastward for those spe- 
cies also in the row of six Midwestern States of North Dakota, 
South Dakota, Nebraska, Kansas, Oklahoma, and Texas. Thus, 
ranges are charted in 17 States. 
The maps have been compiled from various sources, following 
the procedure reviewed in the first volume. These include 
publications, herbarium specimens, field work, and review by 
botanists, foresters, and others. Credit is due many persons for 
their valuable assistance. Maps of vegetation, forest types, 
topography, and landforms have been very helpful in determina- 
tion of lines along borders of ranges. 
The species maps follow the general plan of Volume 1. The 
scale of the base map of the United States is the same, 
1:10,000,000, though the page size has been reduced slightly. 
The second base map, North America, is added for 62 tree 
species whose natural range extends beyond into Canada or 
Mexico. Natural geographic distribution of each species is 
shown as a brown shaded pattern of fine dots on the black-and- 
white base map. Outlying stations are plotted by large or small 
dots. 
Order of maps is alphabetical by scientific name. Common 
and scientific names follow the Forest Service Check List 
(1953), except for several minor changes in nomenclature. 
Notes on ranges are included. At least 21 species have broad 
east-west distribution. Thirteen range from Alaska to the lower 
48 States. Five shrubby species are native from Canada 
southward across the United States to Mexico. The number of 
tree species native in an area obviously increases from north to 
south. The great variation in altitude is one of the most 
significant factors in the distribution of tree species in Western 
United States. 
Rare, local, and endangered species are listed. As mapped, 
about 60 species of minor western hardwoods have relatively 
small range in the United States. Of these, 34 are border or 
peripheral species mostly widespread in Mexico. Among the 26 
species with local distribution are 9 on the endangered list and 5 
on the threatened list. 
