RED MOUNTAIN, ARIZONA: A DISSECTED VOLCANIC 



CONE 



WALLACE W. ATWOOD 

 University of Chicago 



The location and form. — On the peripheral portion of the San 

 Francisco Mountains, and about 30 miles northwest of the village 

 of Flagstaff, Ariz., there is a small tuff cone, locally known by the 

 somewhat appropriate name of Red Mountain. This cone bears the 

 name of Mesa Butte on the San Francisco Mountain sheet of the 

 topographic atlas. It rises between 700 and 800 feet above the gen- 

 eral level of the plateau on which it stands, and at the summit is at 

 least 7,750 feet above sea-level (Fig. i). 



When approached from the southeast or northwest. Red Mountain 

 presents an even, dome-shaped form, such as is common to many 

 of the cinder cones of the region, and if seen from either of these 

 directions it would not attract special attention. On the south- 

 west side a valley has developed, and the material taken from the 

 mountain has been spread out at the base as an alluvial fan. On 

 the northeast side there is a unique exposure, where the mountain 

 has been so cut open that its internal structure is beautifully shown. 

 From a distance (Fig. 2) few details of the exposure can be made 

 out, but a number of layers appear which are roughly concentric 

 and approximately parallel to the profile of the mountain. At closer 

 range (Fig. 3) the concentric layers come out more strongly and 

 they are seen to decline, not only to the right and left, but also toward 

 the observer. 



The material. — The material of Red Mountain consists of vol- 

 canic dust, cinders, lapilli, small crystals and fragments of crystals, 

 a few bombs, many angular blocks, some agglomerate, and a bed of 

 lava which is in part scoriaceous and in part compact. By far the 

 greater amount of the material consists of the smaller products of 

 volcanic eruption. About the base of the mountain, and high on 

 the slopes, there are large quantities of black cinders and lapilli. They 



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