1921] CURRENT LITERATURE 335 
NELSON” has given us a rather extensive account of the geography and resources 
of one of the least known regions of the continent. The larger portion of the 
report is occupied with an account of the exploration of the peninsula from 
north to south. Although 800 miles in length and from 30 to 100 miles in 
width, it possesses a population of little over 30,000, more than half of which 
is found in the extreme north on the delta plain of the Colorado River. Much 
of this sparcity of population is due to the essentially desert character of the 
peninsula as a whole. Rainfall records are very scanty, but show that there 
is rarely over ro inches of annual AS cp pies while over large areas from one 
to five years may pass with practically no . Some idea of the general 
aridity may be formed from the fact that pecshcal three-fourths of the entire 
length of the peninsula there are no forests whatever, only the tops of the 
higher mountains at the northern and southern ends being covered with trees. 
The only extensive forests are those contained in the northern area, where trees 
extend along a narrow belt 150 miles long on the higher slopes of the Juarez 
and San Pedro Martis Mountains, and within this area the merchantable 
timber does not cover more than 400 square miles. re the more important 
species are Pinus Jeffreyi, P. contorta, P. Lombesbtans. Abies concolor, and 
Librocedrus decurrens. Associated with them are other trees and shrubs, the 
Same or similar species to those of southwestern California, often constituting 
a scattered chaparra 
The essentially desert character of the remainder of the peninsula is also 
shown by the inclusion of three-fourths of the entire land area within the Arid 
Lower Sonoran Life Zone and of more than half of the remainder within the 
Arid Tropical Zone. This zonal division also corresponds closely to the three 
main elements of the flora derived respectively from (1) the mountains and 
foothills of southern California, seen in the northern forests and scrub; (2) the 
deserts of the northwestern Sonora and southwestern United States; and 
(3) the lowlands and mountains of the southern Sonora on the mainland of 
Mexico 
Cacti appear to reach a climax in the Lower Sonoran, both in size and 
abundance. In his annotated list of species GOLDMAN” gives over 30 species 
longing to 11 genera, varying in size from the smallest to such large forms 
as Lemaireocereus eruca, with huge, prostrate, caterpillar-like stems 6 or 8 ft, 
long, and the largest of the giants, Pachycereus Pringlei, more than 50 ft. high 
and three ft. in diameter. Many of the associated plants are wv same as as those 
of California, including species of the Yucca, Agave, Fouqueria, Cercidium, 
Parkinsonia, Prick, Covillea, and palms of the genera Washingt onia and 
NELSON, E. ye atte California and its natural resources. Mem. Nat. Acad. 
Sci. 16: ghee pls. 1 2 
Eos os pee records of an expedition to Lower California. Contrib. 
US. Pose ‘Het. 16:309-371. pls. 103-133. Map. 1916. 
