152 LANDS OF THE ARID REGION OF THE UNITED STATES. 
streams fed by the rains and snows of the high table lands and mountains. 
All these streams have a rapid fall in their upper courses, and are here often 
of considerable size; but upon reaching the lower and more level country 
their waters are rapidly absorbed by the porous soil and evaporated by 
the higher temperature. So great is the loss from these causes that some 
streams fail to reach the main drainage channel during the warmer months, 
and all are greatly shrunken in volume. All the arable lands—or lands 
where altitude, slope of surface, and quality of soil permit successful culti- 
vation, if a supply of water can be obtained, and from which lands to 
irrigate, or irrigable lands, may be selected—are in the valleys adjacent to 
the streams. Usually this area in many valleys is in excess of that which 
the water in the streams can irrigate, and choice in the location of lands to 
cultivate is often practicable. In this report I have considered irrigable 
lands to be such only as possess all the necessary qualifications of altitude, 
slope of surface, and fertility of soil, and have, in addition, an available 
supply of one cubic foot of water per second for each hundred acres. The 
great dissimilarity between the valleys makes it desirable to consider the 
drainage basin of each separately, in respect to arable lands, irrigable lands, 
volume of water, and practicability of increasing this supply during the 
irrigating season. 
THE VIRGIN RIVER. 
This stream is in the extreme southwest corner of the area under con- 
sideration. Its branches rise in the Colob Plateau, at altitudes varying 
from 8,000 to 10,000 feet above the sea. It flows in a southwesterly course, 
and joins the Colorado beyond the boundaries of Utah. The smaller 
creeks draining the eastern portion of the plateau unite, after descend- 
ing to an altitude of 5,500 feet above the sea, and form what is called 
the Pa-ru-nu-weap Fork of the Virgin. At and below the junction of 
these creeks, the canon valley in which they flow widens into what. is 
known as Long Valley. There a considerable area of available land is 
found. The soil is excellent, and wherever cultivated yields abundant 
crops. Below Long Valley the stream enters Pa-ru-nu-weap Canon, and is 
simply a series of cascades for 15 miles, descending in this distance from 
