378 Noble — Geology of the Grand Canyon, Arizona. 



Point, where a drop of 4500 feet is accomplished in a distance 

 of a mile and a half. The latter drop is not equaled elsewhere 

 in the Grand Canyon. 



The width of the Grand Canyon in the Shinumo area from 

 Bass Camp to Dutton Point is seven miles ; from Bass Camp 

 to the head of the Shinumo Amphitheater it is twelve miles ; 

 from Havasupai Point to Point Sublime it is five and one-half 

 miles. The latter is the minimum width of the Grand Canyon 

 in the Kaibab division. Even at this, the narrowest point, the 

 width is over live times the depth. 



The differences of climate to be found within the Shinumo 

 area are remarkable. The range in climate between the Kai- 

 bab Plateau on the north rim and the bottom of the canyon is 

 as great as that between the mountains of Colorado and the 

 Mojave Desert. The winters on the Kaibab are extremely 

 severe : from November to April the snow lies deep in the 

 woods, often accumulating to a depth of ten feet ; even in mid- 

 summer the nights are chilly and days delightfully cool. Within 

 the canyon, however, the snow rarely falls below the level of 

 the Esplanade, while on the Tonto platform a fall of snow is 

 practically unknown. The winters in the depths of the- can- 

 yon are mild, and freezing temperatures are rare. From April 

 to October the entire canyon below the Bed Wall concentrates 

 the solar heat, transforming it into a veritable oven ; all day 

 the bare rocks absorb the heat of the sun, becoming so hot as 

 to burn the hand ; by nightfall the wind becomes a furnace 

 blast, and until after midnight the rocks radiate their heat, 

 feeding the hot wind, which blows without ceasing. The 

 effect of the heat, however, is not enervating, for the dryness 

 of the warm wind evaporates all moisture from the body and 

 keeps it cool. The climate of the southern, or Coconino, Pla- 

 teau at Bass Camp is characterized by more open winters than 

 the Kaibab, as well as by warmer summers : the snow in winter 

 rarely accumulates on the surface to a great depth, and as a 

 rule vanishes entirely within three days after a storm ; in sum- 

 mer the days are unpleasantly hot. 



The climate of the Kaibab Plateau is decidedly moist, the 

 precipitation being probably twice as great as that received 

 upon the Coconino Plateau across the canyon ; this is chiefly 

 due to its greater altitude. In winter the precipitation takes 

 the form of snow ; in summer it comes in the form of showers, 

 which occur through the afternoon and evening. Looking 

 across the canyon from Bass Camp on the south rim, almost 

 any summer evening one may see storm after storm sweeping 

 over the Kaibab surface, usually accompanied by violent elec- 

 trical display, while the sky overhead and to the westward 

 over the Kanab Desert remains as clear as crystal. Another 



