K. Bryan — Rock Tanks and Charcos. 



199 



nels on that side of the range. Streams immediately be- 

 gan to cnt headward through this fault scarp, and it has 

 generally been removed. However, in certain ranges, the 

 Estrellas and Tinajas Altas in particular, the new grade 

 has not yet reached the crest of the range, and is sepa- 

 rated from the old by falls, as illustrated in fig. 7. 



yAlfuvial Slope 



• Narrow Canyon 



' Eroded after 

 ! Zad uplifh 



;.'• "•;. 'A 1 1 u v i u m . • V- ;-. 



Broad upland I 



Canyon I 



Eroded after I 

 I s - 1 " uplifr 



lerhary and older 



Fig. 7. Diagram showing production of falls and tanks by renewed 

 uplift of eroded fault-block mountains. 



The famous Tinajas Altas is the only watering place 

 which can be definitely ascribed to this cause, but it is 

 thought that a number of other tanks, including Tule 

 Tank and Heart Tank, were probably formed in the 

 same way. 



Schrader has noted a number of rock tanks on the 

 east flank of Estrella Mountains, Maricopa County, at 

 the elevations of 2,000 to 3,000 feet. 7 The Maricopa topo- 

 graphic sheet shows that in a number of these canyons 

 the stream grades between the elevations of 1,500 feet and 

 3,000 feet are so steep as to be almost continuous falls. 

 Above 3,000 feet the grade is flat and the canyon is wide 

 with gentle slopes. There is thus good evidence that the 

 Estrella Mountains have been rejuvenated by block fault- 

 ing, and that the tanks are plunge pools and potholes 

 associated with falls due to the dissection of the fault 

 scarp. 



7 Schrader, Frank C. : Eeport on the Gila Eiver Indian Reservation, 

 Arizona, as to the mineral or non-mineral character of its lands, 1918. 

 Unpublished manuscript in the files of the Land Classification Board, U. S. 

 Geol. Survey. 



