78 THE UNIVERSITY OF OKLAHOMA 



some soil except near the top where they arc covered by a mass 

 of granite or gabbro. The lighter rains sink into this soil and the 

 water gradually works its way downward into the crevices of the 

 rock and does little or no carrying of materials. During the heavier 

 rains a process of sheet erosion occurs in many places ; the water 

 running down the side of the mountain as rain runs off a roof. 

 As this sheet of water is shallow its carrying power is small and 

 it picks up only the finer material. This is carried downward with 

 increasing ve'ocitjr until it reaches the bottom. A§ the water rushes 

 out over the surrounding plains its velocity is checked and the 

 load of finer materials is deposited. This material slopes away 

 from the foot of the mountain at an angle of usually about 2° or 3° 

 and extends outward to distances of from 500 feet to one-half mile. 

 It is mingled more or less with the surrounding Redbeds material at 

 the contact but can readily be distinguished from it by means of a 

 band-glass as the true Redbeds material is much finer. 



The surface material from the greater part of the igneous area 

 of the Wichita Mountains is being carried by the streams into the 

 Red River and the North Fork of the Red. These streams rur., as 

 a rule, in narrow channels from 10 feet to 40 feet deep. During the 

 greater part of the year the volume of water in them is. so small 

 that only the finer sediments are carried down, but at times of 

 high water the channels are filled and often overflow. At sucn 

 times the streams have great cutting and carrying power and the 

 finer material that has accumulated during the low water is rushed 

 out to the Red River and the North Fork of the Red River. These 

 heavy rises last usually only a short time so that only a relatively 

 small amount of coarse material has time to find its way to the 

 main streams after the finer material has been disposed of. These 

 floods are often local and so when a tributary dumps its load into 

 the main stream there is usually not sufficient volume to carry it 

 and this results in the local filling up of the bed of the main 

 stream. This keeps the main drainage channels in an overloaded 

 condition and gives them the appearance of aggrading streams while 

 in reality the whole area of the watershed is being rather evenly 

 degraded. A part of the material in the main channels is rushed 

 down stream with each period of high water and is again deposited 

 as the water goes down. During these periods of high water the 

 river cuts through its sand bed in many places to the rocks from 

 30 feet to 50 feet below and abrades them to some extent. As the 

 flood goes down these holes are again gradually filled as the stream 

 deposits its load. Thus the sand and silt of he river bed is 

 carried in successive stages toward the mouth of the stream. 



