410 The University Science Bulletin. 



cisco mountains in Arizona, or laccolithic intrusions like the Henry 

 mountains in southern Utah. These are not important in the aggre- 

 gate, but are striking on account of contrast. 



All of the Colorado plateau region is arid or semiarid. There is 

 little rain, and most of that which does come falls during a small 

 part of the year and in torrential showers. Much of the character- 

 istic topography and the aspect of the country in general is due 

 chiefly to this. 



THE HIGH PLATEAUS OF SOUTHERN UTAH. 



The features and the conditions which are broadly typical of the 

 Colorado plateau as a whole find especially characteristic expression, 

 and, indeed, culminate in the south central part of Utah and adja- 

 cent portion of Arizona. From the Grand canyon of Colorado river, 

 the most profound and prodigious of the canyons, the stratified 

 rock platforms rise tier on tier like gigantic stairs ascending north- 

 ward. The top "stairs," in southern Utah, have an elevation of 

 more than 10,000 feet above sea level, and comprise the so-called 

 high plateaus. It is almost inevitable that this lofty plateau 

 country, so closely adjacent to the deepest of the canyons, should 

 be intricately dissected by tributary canyons. The high plateaus 

 and adjoining region may therefore be specially designated as the 

 "canyon lands." Travel is by tortuous and extremely toilsome 

 routes, now in the depths of a profound abyss, now crossing a pla- 

 teau spur of mountainous proportions. Some areas are absolutely 

 inaccessible, and large districts are almost unexplored. Population 

 is confined to a very few of the accessible valleys where irrigation 

 permits cultivation of a little of the land adjacent to the water 

 supply. Aside from these outposts of determined agricultural skill 

 and industry, the region is traversed only by occasional cattlemen, 

 prospectors or explorers. 



CLIMATE. 



The two main features which characterize the climate of southern 

 Utah and affect more or less directly the life of the region, as well as 

 physiographic processes, are dryness and temperature variation. 

 In part of the area rainfall is less than five inches in the year, and in 

 all of it the average is less than ten inches per year. In general, 

 there is most rain in the three summer months, July August and 

 September; and least rain in the spring months, April, May and June. 

 The fall and winter months have an intermediate rainfall. The 

 effect of the dry spring season, when most plants begin to develop 

 rapidly and when many of the animals, especially the insects, pro- 



