44 



map (Fif?. 2) shows that tho isotherms of 70 degrees for July and of HO 

 degrees for January cross near San Francisco and si)read widely apart, 

 bounding a belt which Ix'lon.irs to the torrid zor.e in sunmur and the frigid 

 zone in winter. The climate is best characterized as intemi)erate, having 

 an annual range of 40 to GO degrees. Maximum temperatures of 110 degrees 

 and mininuun of -50 degrees are not unusual. The belt is swept by a 

 procession of cyclones and anticyclones which bring rapid changes from 

 cool and dry to warm and wet and vice versa, two or three times a week. 

 The weather is perhaps the most variable and uncompromising in the 

 world. Cold waves and hot waves intensify the seasons and give everybody 

 something to talk and read about. The atmosphere furnishes a penietnal 

 turkish bath, running the gamut from hot to cold and cold to hot in the 

 most stimulating and irritating manner. Our European friends say that 

 American hustle and restlessness and the strained expression on our 

 faces are due to the uncertainty and intensity of American weather. 



The eastern half of the intemperate belt is saved from aridity by 

 cyclonic winds from the gulf and Atlantic, which carry a rainfall of 2(» 

 or more inches to Hudson Bay. The western half catches its moisture 

 as catch can and i)nts up with the driblets left from the load dropped on 

 the eastern plains or the western mountains. The line near the 100th merid- 

 ian where the 20-inch isoihyet and the 2,000 foot isohyps coincide is one ol" 

 the most strongly marked natural boundaries in tlie world. It is the west- 

 em limit of forest, prairie, agriculture without irrigation and dense popula- 

 tion. The medial belt of North America is divided into three pairs of 

 ],rovinces, tlie Pacific. Interior, and Atlantic. The simplest is the In- 

 terior," including the Arizonan, already noticed. 



The Interior province is composed of two i>lateaus separated by the 

 broad system of the Rocky ninunlains. There is not a square mile in it 

 below 2,000 except in llie luwcr Cdhimbia valley, and most of it lies abov(> 

 all but the smnmits of the Aiiiialadiians. On the west the smaller Co- 

 Iniiihia iilalc.-ni is a frozen sea of lava, trcuclud by tlu' Snake and Colnni- 

 bia rivers in gl(M)my canons. Most of the scant rainfall sinks into the 

 crevices to reai)pear along the cafion walls in voluminous springs. The 

 dominant plant format io:i is sagebrush, wliicli is neither grass ntn- slirnb 

 nor tree, but just artemesia. The t'astern plateau, connnonly known as the 

 fireat Plains, but better ch.ariicteriztsl as the High Plains, is nearly 2,000 

 miles long and 800 to .'')0(» iiiilcs wide. It is liniken here and there by 



